One Piece Wiki:Guidebook/Category Guidelines

Categories are lists containing pages that all fit into a certain group. They play an important role in site navigation, and thus must be handled with care and accuracy.

General Rules

 * Make sure to read the category page if you are unsure about placing a category on a page. Some categories have specific conditions that pages must meet before they can receive that category. For example:
 * Category:Children is for characters who ONLY appeared in the story as children.
 * Category:Former Pirates is only for people who stopped being pirates for reasons other than death or capture.
 * Category:Swordsmen is only for people who have actually used a sword; it is not for people who have simply been seen carrying swords.
 * Try to avoid creating overly specific categories that only have very few pages in them, especially if those pages would fit in a more general category that already exists.
 * If you are creating a specific category from a more general category, the new category must have at least five pages in it, otherwise its pages will be moved back to the general category.
 * This does not apply to categories that would not fit in any general category, but there should be no categories with only one page in them. Please note, though, that even if a new category is unique it may still be considered too minor by other editors.
 * Categories must be clearly defined. It should be easy to determine whether or not something meets the requirements to be in a category without being speculative.
 * Categories should note major traits. We should not have categories for minor traits, such as hair color, that are superficial to the story.
 * The name of a category should always be plural, unless it is the name of a group (such as Category:Worst Generation).
 * If your creation or addition of new categories is disputed, talk about it on the category talk page, do not edit war and add the categories back.
 * If you are thinking about performing a major category overhaul, proposing it on a forum is strongly recommended. Commencing disputed large-scale projects without input may get you in trouble.

Character Pages
These are the kinds of categories that should go on character pages, in this order:
 * The character's race or species. See Category:Characters by Type.
 * The character's gender. See Category:Characters by Gender.
 * The character's occupations, both present and former with present coming first. See Category:Characters by Occupation.
 * Groups that the character is or was part of (note that putting a character under a group category may also put them under an occupation category: if one receives Category:Straw Hat Pirates, then they will also be under Category:Pirates, meaning there is no need to put the Pirates category on their page. See the Parent Categories section for more information on this). See Category:Characters by Group.
 * Abilities that the characters possess, including fighting styles, Devil Fruits, Haki, and weapons. See Category:Characters by Ability.
 * Locations where the character has resided. See Category:Characters by Location.

Characters can also receive Category:Deceased Characters if they are dead, Category:Children if they have only been seen as children, and Category:Mentioned Only Characters if they have not been seen in the story yet.

Parent Categories
Parent Categories are categories that contain category pages. By doing this, anything categorized under a more specific subject can also be categorized under a general subject without having redundant categories. For example, everyone under Category:Straw Hat Pirates is a pirate, and so that category page is given Category:Pirates. Thus, by putting the Straw Hat Pirates category on a page, the subject will also be categorized under Pirates.

In order for a category page to be given a parent category, every page in that category must also belong in the parent category. Thus, you cannot make Category:Devil Fruit Users a parent category of Category:Big Mom Pirates because not everyone in the Big Mom Pirates is a Devil Fruit user.