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 would be considered a parent category to the overly specific category.
 * 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 purely superficial to the story.

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 thus would be under 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.