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.
 * 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, and Haki. See Category:Characters by Ability.
 * The location that the character was born in as well as the location where they first debuted. 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.