Categories should typically include any notable subjects prominently featured within a file, as well as further contexts where necessary (e.g. "Episode Cover", "Volume Cover"). For example, the image to the left would be categorized: Guts, Dragon Slayer, Berserker Armor, Cannon Arm, Volume Cover, as Guts, the Dragon Slayer, Berserker Armor, and Cannon Arm are all featured prominently and the file is indeed a volume cover.
Ultimately, refer to files similar to your own and see how they are named and categorized if you are unsure how to do so. Files that fail to adhere to the above stand a high chance of being deleted.