A few years after the events of a solar eclipse, one that foretold the coming of an angel of darkness, a lone swordsman walks into a bar where an elf is being tormented by a group of bandits. When the bandit leader threatens to kill a red-haired youth requesting membership, Guts beats the gang and takes his leave with the freed elf, named Puck, following him. Eventually, Guts reluctantly accepts being picked up by an old priest named Adolf despite warning him that he is constantly hunted by evil spirits. After sunset, waking up after a nightmare, Guts and the wagon are attacked by spiritually-possessed skeletons with Adolf and his daughter Collette killed off during the assault. Guts spent the night fighting the skeletons and then a tree animated by pagan spirits. Despite Puck attempting to console Guts, who hears the spirits' constant taunting, the swordsman scoffs the deaths of Adolf and Collette as proof of their weakness. Guts attempts to leave before he is surrounded by the Holy Iron Chain Knights, who have been tracking him since the day they investigated the events of the solar eclipse and came across the remains of mutilated men in a pool of blood.
Despite his fatigue, Guts easily kills some of the Holy Iron Chain Knights, who have been sent by the Church of the Holy See to capture him. When Guts finds himself overwhelmed by their vice-commander Azan, he attempts a dash at the knights' leader Farnese de Vandimion. But Guts is wounded by a cross arrow bolt, followed by a piece of wood, and falls unconscious. Once stripped of his gear and brought to the knights' camp, Guts is interrogated by Farnese for answers that include the mysterious demise of the Band of the Hawk, having found the mercenary group's bloodied remains after the solar eclipse. As Guts mocks on her authority and her faith, Farnese whips him until Azan arrives. Guts is placed in a cage soon after, freed by Puck at nightfall as the spirits start to awaken. Guts enters Farnese's tent to recover his equipment while finding her in the middle of self-flagellation, deciding to take her hostage for a quick escape. The other knights work to cease the fire Guts started while Serpico gives chase after the swordsman, the knight finding himself surrounded by pursing spirits.
The spirits pass Serpico and chase Guts to an abandoned mansion as he tells Farnese, who is unable to see them or Puck, that they are her god's "miracles". Guts quickly gets Farnese and the horse inside as the spirits possess hounds and use them to break in. Guts manages to kill the dogs before facing the estate's kennel master: an Apostle who mounted the remains of the woman he cared for and unknowingly sacrificed on the foyer. Guts defeats the Apostle and kills him after attempting to interrogate him on the God Hand, searching for Farnese after she fled in terror. Guts finds Farnese as she was about to violated by the possessed horse, killing the creature as its act brought back horrible memories. Farnese then ends up being possessed herself and forced to act her lust before sun rise. Serpico retrieves a mortified Farnese and escorts her back to their camp while allowing Guts a reprieve. Meanwhile, in the city of Windham, the King of Midland passes away after a vision of Griffith returning while a foreign army comes to his land.
After having a vision of Casca being burned at the stake, Guts returns to Godo's hut to check in on her. After he arrives, he receives the terrible news of Casca's disappearance. Guts struggles with his past demons along with the growing evil within his soul as he fears Casca is the only remainder of his sanity left. After talking with Rickert at the Hill of Swords, Guts resolves himself. Godo arms Guts with new armor and a reforged Dragonslayer to prepare him for his new journey. Meanwhile, the Holy Iron Chain Knights accompany the Grand Inquisitor's caravan as an escort. They are soon attacked by rebels who seek revenge against the Holy See, but are swiftly captured by masked inquisitors. The Grand Inquisitor himself, Mozgus, steps outside to lecture the rebels before having the survivors executed on breaking wheels. Unbeknownst to everyone, Casca is cluelessly traveling with the Holy Iron Chain Knights.
Guts encounters and kills a party of Kushan scouts, saving the life of Isidro who follows him out of admiration. Meanwhile, catching some starving refugees attacking a food wagon, Mozgus brings a refugee and her baby to the abbey; although her baby is cared for, Mozgus tortures her for her blasphemy. In the refugee's camp, Luca keeps Casca disguised as her bandaged sister "Elaine" and shares her payment from clients including the knight Jerome with her fellow prostitutes. One of them, Nina, worries about her disease while fetching water with Casca, not noticing the spirits stalking them. Isidro catches up with Guts, when they are attacked by more possessed corpses.
As Casca is saved by the monstrous fetus, Guts encounters the mysterious Skull Knight for the first time in years since the Eclipse. Guts is disturbed to learn that the God Hand are using St. Albion as the site of a horrific ritual to restore Griffith's corporeal form, refusing to accept it as fate as he resumes his run towards the city with Isidro still following. The next day, as Farnese finds herself struggling with her faith, Nina meets her reoccurring customer Joachim and tests his love for her by having him come with her to a midnight orgy held by the pagan cult's goat-headed leader. Joachim gradually engages until learning that the pagans are cannibals and runs off before he was seemingly killed. Nina breaks down before seeing Luca, who disciplines her before forgiving her and then learning that Casca followed her. Casca nearly gets raped by the pagans who found her until they were possessed by spirits. Luckily, Casca was saved by the fetus and the surviving pagans assume she is a witch.
Returning to camp while fearing persecution, Luca finds Pepe arrested by pagan hunters and tries to defend her before they are saved by Guts, who just arrived to St. Albion and dispatched the hunters while asking for Casca's whereabouts. Luca takes Guts to Casca's tent upon noticing his brand, only to find that a fearful Nina abducted her. But Isidro finds Nina as she and Casca are captured by the pagan cult, who intend to marry the "Black Witch" to the Great Goat while Nina is be to sacrificed. After the Holy Iron Chain Knights are led to the pagans' cave by Joachim, Farnese finds herself in another unnatural situation when they are attacked possessed cultists who slaughtered their own. During the ensuing chaos, as Isidro attempts to save Casca, the Great Goat is transformed into a satyr-like Apostle by a mysterious observer and kills anyone within reach. When the Great Goat then attempts to consummate his marriage, Guts arrives at the last second to save Casca as the two see each for the first time in two years.
Having arrived just in time, Guts saves Casca as the two are reunited. However the reunion is cut short once the Great Goat attacks Guts. Guts battles the fearsome Apostle as the Holy Iron Chain Knights retreat with Isidro, Puck and Nina escaping with Casca. Guts succeeds in killing the Great Goat with the help of Rickert's miniature bombs while Casca and Nina are once again confronted by the Holy Iron Chain Knights, who capture them. Guts makes his way out of the cult's cavern only to be ambushed by Serpico on a cliff side. Serpico reveals he has been seeking to kill the Black Swordsman and has prepared the duel in his favor due to the terrain and Guts' current state. Guts is surprised by Serpico's remarkable speed and agility but manages to win the encounter once he crushes Serpico's sword with his iron prosthetic. Serpico escapes by using Guts' miniature bombs against him while Guts confronts Isidro about Casca's disappearance. Guts, Isidro and Nina return to the Tower of Conviction while Puck searches the cells inside for the duo. Nina is taken first by Mozgus' disciples to be tortured first for information on the "Black Witch", leaving Casca behind. All the while, a mysterious egg-shaped Apostle dwells at the top of the Tower; waiting for its plan to come to fruition.
After Nina named her as the witch he seeks, Mozgus places Casca in an iron maiden upon seeing her brand. But it causes the spirits of the tortured to manifest as a flesh-eating blob of blood with almost everyone able to escape. While Luca and Isidro use Jerome to free Nina, Guts forces Farnese to take him to the torture chamber where Puck tells him Casca is still alive. With Casca trapped inside it, the blood moves up the tower as Mozgus' group barricade themselves in the chapel. But they are then transformed by the observer, Mozgus deeming it divine providence as he burns away some of the blood with his flames. Though he freed Casca and saved Luca's group, Mozgus intends to have the former burned at the stake while his men attack the latter. Luca sacrifices herself so Jerome can save Nina, only to be saved by the Skull Knight as he was about to attack the observer. Guts arrives soon after and battles three of Mozgus' men as the inquisitor's group all sprout wings.
Luca is spirited away by the mysterious observer, who reveals himself to her as a Behelit-like Apostle self-dubbed the Egg of the Perfect World. The Egg tells Luca his story and his long observation of everyone in St. Albion, detailing his ideals and the event to soon occur before fleeing from the Skull Knight. The Skull Knight takes Luca to safety as the living mounds of starved corpses rise up. Back in the Tower of Conviction, while the other disciples deal with Guts, Mozgus and the Twins fly off with Casca. While Guts manages to kill Mozgus's disciples, the possessed blood causes the tower to partially collapse with Guts enduring the cave-in to see the chaos unfolding in the slums. Mozgus uses his powers to keep the corpses at bay while the refugees proceed to build a pyre to burn Casca on. Guts sees this while noticing the four senior members of the God Hand manifesting through the blood.
As Luca walks back to St. Albion after the Skull Knight took her to the outskirts, the Egg of the Perfect World swallows the dying Demon Child out of sympathy before resuming his climb up the Tower of Conviction. At the same time, enlisting Jerome and Nina's help, Isidro uses a makeshift pulley system to free Casca as she was about to be burned alive. Mozgus nearly catches them after forming a barrier to keep the corpse mounds at bay when Guts leaps off the tower and impales the inquisitor. But Mozgus's bible shielded him from the attack while he fully transforms. As Isidro's group eliminate the last of Mozgus's disciples, the inquisitor's flame barrier dies out as he attempts to give Guts a chance to recant. But Guts instead uses his miniature bombs to blow apart the unprotected chink in Mozgus' armored body to land the death blow. After a brief reunion with Casca, the corpses manage to flood into St. Albion as Guts gives his group torches so they can outlast the few remaining hours of night.
Guts and his group fend off the flood of corpses with their fire while Luca saves Nina down below the tower. Meanwhile, the Egg of the Perfect World collects the energy of St. Albion's souls and sacrifices himself to resurrect Griffith in a corporeal form. The Tower of Conviction collapses, killing everyone inside as the sun rises. Guts and the others collect themselves, but are quickly surrounded by Silat and his Kushans. The Kushans are immediately repelled by Nosferatu Zodd who bursts through the rubble and marches to a nearby hill. At that moment, everybody ceases fighting to witness Griffith arising from the ground as Zodd kneels before him. Guts goes to immediately attack, but is stopped by Casca. As the Kushan army proceeds with its invasion, Zodd and Griffith escape into the skies while Guts, Puck and Casca ride to Godo's on horseback. Isidro departs on his own while Luca mourns the death of the Egg. While Nina reunites with Joachim, Farnese leaves her faith behind; deciding to follow Guts as Serpico travels with her.
Guts and Puck take Casca back to Godo's home to find Godo has died. Griffith appears, wanting to know how meeting Guts would feel, and is pleased that he feels nothing and can continue to pursue his dream. Guts attempts to kill him but is stopped by Zodd who he duels fiercely until Zodd's sword shatters against the Dragonslayer. Zodd destroys Godo's iron mine and home. Griffith ponders whether the feelings he has are caused by the Demon Child who became his vessel and saves Casca from being crushed by falling rocks. He then offers Rickert a place in the new Band of the Hawk before leaving with Zodd. Guts reveals to Rickert how Griffith took his eye and left arm, sacrificed their comrades and raped Casca but refuses Rickert's offer to help get revenge. Knowing he cannot lock Casca away to keep her safe, and not wishing to leave her behind, Guts decides to take her to Puck's home instead. Elsewhere in the kingdom Kushan soldiers destroy a castle, kill the citizens and capture the women until Griffith arrives and is hailed by the people as the Hawk of Light.
A young witch, Schierke, watches Griffith from a distance. While tracking Guts, Serpico remembers how Farnese took him in as her servant, though she abused him terribly. Serpico learned he was the illegitimate son of Farnese's father and was therefore her half-brother, eventually becoming her bodyguard. Upon learning she was engaged to a member of the royal family Farnese tried and failed to seduce Serpico and set fire to her family mansion before joining the Holy Iron Chain Knights, eventually forcing Serpico to burn his mother as a witch. With their brands being so close together more powerful demons are attracted to Guts and Casca who tempt Guts to kill Casca to get closer to Griffith. Guts' rage overwhelms him and he hurts Casca, destroying her trust in him and she runs away. She is caught and almost raped by bandits, causing her to remember being raped by Griffith and she slaughters the bandits before attacking Guts. Guts is again overwhelmed by rage and almost rapes Casca before regaining control of himself. They are later found by Isidro, Farnese and Serpico who ask permission to accompany Guts on his mission.
A Kushan occupied city is liberated by Griffith and his new Band of the Hawk: Composed of Nosferatu Zodd, Sir Locus the Moonlight Knight; the exiled Bakiraka assassin Raksas, Grunbeld the Giant and Irvine the Archer. Joined by the clairvoyant girl Sonia, the Hawks later dealt with a Kushan legion that overwhelmed Midlanders under the command of Mule Wolflame. Though Mule was upset to learn Kushan prisoners are given a choice to join Griffith's army, and that some of the army's members are demonic cannibals, Mule was mesmerized by seeing Griffith holding final rites for the fallen whose spirits depart while bidding farewell to their families. Mule is overcome with emotion from being in Griffith's presence, immediately pledging his loyalty to him. Meanwhile, after Farnese cuts her hair to prove her resolve, Guts allows her, Serpico, and Isidro to travel with him as he no longer trusts himself to protect Casca on his own. Guts does warn them that traveling with him means they would not be able to sleep at night, the group later fending off attacking specters after nightfall.
Farnese becomes depressed after Casca disappears and she gets lost in the forest trying to find her. A shepherd warns Guts' group about an imminent battle between Griffith's army and the Kushans and also about trolls infesting a nearby area. Serpico admits to Guts he desires to kill him in a fair duel, but as long as Farnese desires to stay with Guts he will treat him as an ally. Isidro practices dueling with Guts. A group of trolls attack but are driven away by the witch, Schierke, whom Isidro manages to insult, and her elf companion, Ivalera, before disappearing. Casca continues to be afraid of Guts and becomes attached to Farnese. They come across an old man whose village is being attacked by trolls, but as the local lord has taken his army to support Griffith the villagers are hoping to find help from a witch rumored to live nearby. Almost immediately they stumble upon Schierke's house as Casca and Guts brands allow them to pass through her protective barrier. Guts mistakenly believes Schierke's earth golems are ghouls and destroys several of them before Schierke reveals herself as an apprentice to the elderly witch Flora who has been waiting for Guts and Casca to arrive.
Revealing an old friend of hers mentioned Guts and Casca would come to her abode, Flora learns of the plight befalling Enoch Village. But due to her failing health, Flora offers Morgan the aid of her apprentice Schierke to deal with the trolls. Flora asks Guts to aid Schierke, offering him a spell that would temporarily cloak him and Casca from being attacked by specters. During the dinner that followed, Flora explains their plane of existence exists alongside the Astral World, whose many layers contain various supernatural beings, and Realm of Ideas which all creation is derived from. Guts later shows Flora the Behelit and is told that it's a gateway to link the physical world with the layer where the God Hand dwell, learning its senior members were once human like Griffith and they answer to a higher power within the deepest layer of the Astral Plane. Schierke, overhearing Guts's talk with Flora, assumes Griffith is the fifth angel prophesied by the Holy See while told that he was the once who branded Guts. The next day, Guts's group receive magical weapons. Serpico receives a cloak and sword imbued with Sylphs, Isidro a dagger imbued with Salamanders, and Farnese a silver shortsword along with silver chainmail tunics for herself and Casca as added protection from evil creatures. Guts turns down accepting a battle axe before he and others leave for Enoch Village, Flora meeting up with her friend: The Skull Knight, who requests a favor regarding Guts.
Guts group arrive at Enoch Village but are turned away by the priest who claims that Schierke is merely a child in a costume, but allows them to stay when Guts claims Casca is a religious pilgrim. Isidro trains by himself and talks with Morgan about his past and Isidro's dreams for the future. Schierke is accosted by children who throw rocks at her for being a witch. Schierke expresses distaste of the local church which was deliberately built on the site of a spirit temple, along with many other temples replaced by churches in an attempt by the Holy See to expand their authority. This included chasing the witch Flora from the village, banishing her to the forest. Guts points out she can always choose not to help the village if she wants to. The trolls attack and Schierke summons everyone to the church for safety. Guts, Farnese, Serpico and Isidro fight the trolls while Schierke shows concern about the mysterious source of Guts strength and of the dark shadows that cling to the Dragonslayer. Schierke begins to cast a spell from the church roof, angering the priest who tries to stop her, only to end up trapped on the roof along with Schierke, Farnese and Casca. While fighting a troll Isidro overbalances trying to swing his sword one-handed and Morgan is injured saving him from the trolls. Schierke finishes casting her spell, summoning four Guardian Angels whose protective light crumbles the trolls to ashes and heals Morgan's injuries.
With most of the trolls dead the village comes under attack from a giant Ogre. Guts fights the ogre but is attacked by a Kelpie from the nearby river. Serpico fights alongside Guts, pitting his wind magic against the Kelpie's water magic. Schierke sends her mind into the spirit realm and senses the spirit temple the church was built upon, originally a temple of Undines, powerful water spirits. Schierke allows herself to be possessed by the river spirit the Lady of the Depths, who channels magic through Schierke to flood the river, washing the trolls, kelpie and ogre back into the underworld. However the magic is too powerful and Schierke is unable to pull her mind back from the spirit realm or break the spell flooding the village. Ivalera has Farnese use Schierke's staff to help bring her back. Just as Schierke returns Casca and Farnese fall into the water and are swept away. As the villagers celebrate Schierke tracks Casca and Farnese with magic and senses that they have been captured by more trolls. Despite the villagers gratitude Schierke feels responsible for the destruction caused by her inexperience as a witch. She receives permission from the priest to build a shrine in the village to appease the angry water spirits. Isidro receives a smaller sword as thanks from Morgan that is easier for him to fight with. Serpico's injuries force him to remain in the village while Guts, Schierke and Isidro immediately leave to rescue Casca and Farnese.
Schierke realizes they have stumbled into a dangerous part of the Astral Realm known as Qliphoth. She telepathically communicates with Farnese and Casca in the trolls cave where the trolls are raping human women, forcing them to become pregnant and then devouring them after they give birth to troll offspring. Farnese protects Casca until Guts and the others arrive. Guts fights the trolls alone while the others help the women escape. Slan, a member of the God Hand, appears and overpowers Guts. Schierke begins a spell to seal the cave hoping that Guts escapes before she finishes. Slan torments Guts sexually and asks if he would be willing to become an Apostle like Griffith did. At that moment the Skull Knight appears to stop Slan, who reveals that Griffith is the reason the realms are merging. While she is distracted Guts shoots her with the cannon in his arm. Isidro proves himself in battle, using his salamander dagger and short sword to kill a giant troll. Slan heals herself but the Skull Knight urges Guts to use the Dragonslayer, made stronger by all the evil souls it has destroyed. He impales Slan who kisses him then disappears, promising they will meet again. Schierke finishes her spell and is possessed by an earth spirit, the Lord of Rotting Roots, who collapses the cave with Guts still inside. The Skull Knight uses his Sword of Actuation, forged from the behelits of apostles he has killed, to cut a way out of the cave. Qliphoth vanishes back into the Astral Realm and the women are taken back to Enoch Village. As Guts watches his friends he admits that he is glad he has comrades again.
Flora reveals a suit of Berserker Armor as guarded over the years. Griffith's demon soldiers break through her barrier, so the Skull Knight rides out to meet them. Guts suddenly collapses as Slan had damaged his soul, but he manages to keep walking and Schierke is astonished that Guts survived against an Apostle. Meanwhile. Schierke senses that Flora's barrier has disappeared and the house is now on fire. Guts rushes to aid the Skull Knight in battle against Zodd and Grunbeld while Schierke and the others rush to find Flora. Grunbeld insists on dueling with Guts while Zodd fights the Skull Knight. Flora allows herself to be consumed in the fire but first instructs Schierke to give Guts the armor. In his weakened state Guts cannot fight and Grunbeld breaks his ribs. Schierke's earth Golems come to Guts' rescue, distracting Grunbeld and allowing Guts to flee. Despite knowing the incredible risks involved Schierke encases the near lifeless Guts within the armor, allowing him to re-join the battle and he slays several demons with ease. Guts is aware that his body is severely damaged but no longer cares about pain while the armor awakens a wolf like entity called the Beast of Darkness.
With the armor removing his limitations Guts unleashes all his strength, destroying Grunbeld’s shield and hammer and wounding him. Schierke explains that as Guts is fighting without limits he is tearing his own body apart, and while the armor removes his pain he will eventually bleed to death. Grunbeld transforms into his Apostle form, a dragon with corundum scales. Guts stops a blow from Grunbeld’s tail and cracks the scales on his face with one swing. Schierke casts her mind into the spirit realm and sees Guts ego trapped inside the Beast of Darkness, but a spell cast by Flora has prevented Guts ego from vanishing. Schierke reminds him of his love for Casca and Guts awakens. He flees from Grunbeld and saves his friends while Flora’s spirit holds Grunbeld back with spirit fire. In Windham, underground resistance meet with Laban of the Midland Arklaw Knights to ask his help in rescuing Princess Charlotte. They are attacked by demons but are saved by Irvine the Archer and Sir Locus for an unknown reason. A month later Guts has healed but still wears the armor. Schierke fears if he has to fight again the armor will kill him.
Guts party resume their journey to Puck’s home, an island called Skellig, half in the normal world and half in the astral plane, a home to both elves and mages. Farnese asks Schierke to teach her to use magic. The Skull Knight warns Guts of the effects of using the Berserker Armour and it is suggested that he was the armor's previous wearer. He also reveals Griffith is targeting witches like Flora as threats to his power and that Hanafubuku, the Fairy King of Skellig, may be able to return Casca’s sanity. At night they are attacked by giant demonic alligators. Schierke casts a protection spell whilst Guts, Serpico and Isidro fight the alligators. Guts struggles to keep the Beast of Darkness under control. Serpico manages to kill the Kushan mages controlling the alligators, but another mage causes them to be attacked by a sea monster. Guts loses control and the Beast takes over, activating the armor and reopening his newly healed wounds while allowing him to violently kill the sea monster. The Beast almost attacks his friends but Schierke manages to awaken Guts at the last second. Guts becomes furious at himself for losing control again.
Guts and his friends approach the city of Vritannis where Isidro upsets Schierke about her witch’s clothing. Schierke learns that Vritannis traded in Kushan slaves, but all the slaves have been hanged as religious enemies of the Holy See. She is seen cremating the Kushans by Sonia who expresses admiration that Schierke helped release their souls. She and Schierke bond over their experiences not fitting in with normal people until they both found someone who accepted them, i.e. Griffith and Guts. Schierke stops pirates from kidnapping Kushan children and is saved by Isidro who had been trying to find her. Isidro uses his new sword to skilfully fight the pirates until Mule Wolflame arrives searching for Sonia and they defeat the pirate captain, all secretly witnessed by Guts. Sonia asks Schierke to accompany her but Schierke turns her down to stay with Guts. Sonia warns Schierke to leave Vritannis quickly and shows her a vision of Vritannis burning. Later Schierke dresses in human clothes and she, Casca and Farnese are protected from drunken soldiers by Guts. Schierke is happy that while she may be surrounded by human suffering she can continue to smile with her new friends.