- Onimai: I'm Now Your Sister!
- One: Kagayaku Kisetsu e
- Onegai My Melody
- Orochi, the Eight-Headed Dragon
- Okko's Inn
- Oomuro-ke: Dear Friends
- Opus.COLORs
- Okami-San and Her Seven Companions
- Ore ga Suki nano wa Imouto dakedo Imouto ja Nai Specials
- Ooya-san wa Shishunki!
- Otaku Elf
- Orient Part 2
- Ore no Sora Keiji-hen
- Orenchi no Furo Jijou
- Orient
- Ore no Nounai Sentakushi ga, Gakuen Love Comedy wo Zenryoku de Jama Shiteiru OVA
- Osamake: Romcom Where The Childhood Friend Won't Lose!
- Otaku no Seiza
- Oreshura
- Oshiete Mahou no Pendulum: Rilu Rilu Fairilu
- Otaku no Video
- Otome Game no Hametsu Flag shika Nai Akuyaku Reijou ni Tensei shiteshimatta... OVA
- Overlord
- Our Last Crusade or the Rise of a New World
