The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- Novus Orbis Librarium (33 members)
- Nox Nyctores (13 members)
- Nox Nyctores Wielders (26 members)
- Nu-13 (562 members)
- Observers (29 members)
- Ogawa, Kazuya (1 member)
- Old Gate (12 members)
- Oliver (3 members)
- Onlookers (4 members)
- Order (6 members)
- Organizations (29 members)
- Orie (27 members)
- Orient Town (48 members)
- Ozawa, Riku (10 members)
- Pages using Tabber parser tag (70 members)
- Pages using deprecated source tags (4 members)
- Pages using duplicate arguments in template calls (4 members)
- Pages with broken file links (11 members)
- Pages with ignored display titles (4 members)
- Pages with reference errors (2 members)