- OniAi
- OniAi Specials
- Onigiri
- Onimai: I'm Now Your Sister!
- Onimai: I'm Now Your Sister! (Uncensored)
- Onimomomomo
- Onimusha
- Onipan!
- Only Yesterday
- Onmyo Kaiten Re:Birth Verse
- Onmyouji
- Onyankopon
- Ōoku: The Inner Chambers
- Oomuro-ke: Dear Friends
- Oomuro-ke: Dear Sisters
- Ooya-san wa Shishunki!
- Open Your Mind
- Operation Han-Gyaku-Sei Million Arthur
- Operation Han-Gyaku-Sei Million Arthur 2nd Season
- Opus.COLORs
- Orange
- Orange: Mirai
- Ore ga Ojousama Gakkou ni "Shomin Sample" Toshite Gets♥Sareta Ken Specials
- Ore ga Suki nano wa Imouto dakedo Imouto ja Nai Specials
- Ore no Nounai Sentakushi ga, Gakuen Love Comedy wo Zenryoku de Jama Shiteiru OVA
- Ore no Sora Keiji-hen
- Ore wo Suki nano wa Omae dake ka yo: Oretachi no Game Set
- Oreca Battle
- Orenchi no Furo Jijou
- Oreshura
- ORESUKI Are you the only one who loves me: Game Over
- ORESUKI Are you the only one who loves me?
- Orient
- Orient Part 2
- Origin: Spirits of the Past
- Original Dirty Pair: Flight 005 Conspiracy
- Orochi, the Eight-Headed Dragon
- Osake wa Fuufu ni Natte kara: Yuzu Atsukan
- Osamake: Romcom Where The Childhood Friend Won't Lose!
- Oshiete Mahou no Pendulum: Rilu Rilu Fairilu
- Osomatsu-kun (1988)
- Osomatsu-san 3rd Season
- Otaku Elf
- Otaku no Seiza
- Otaku no Video
- Otherside Picnic
- Otherworldly Evil Monarch
- Otogi Zoshi: The Legend of Magatama
- Otome Game no Hametsu Flag shika Nai Akuyaku Reijou ni Tensei shiteshimatta... OVA
- Otome Youkai Zakuro Picture Drama
- Otona no Bouguya-san 2nd Season
- Our Dating Story: The Experienced You and The Inexperienced Me, Kimizero
- Our Home's Fox Deity
- Our Last Crusade or the Rise of a New World
- Our Last Crusade or the Rise of a New World Season 2
- Our love has always been 10 centimeters apart.
- Ouran High School Host Club
- Outbreak Company
- Outburst Dreamer Boys
- Outlanders
- Outlaw Star
- Oval x Over
- Over Drive
- Over Goddess
- Over the Divine Realms
- Over the Sky
- Overflow (TV ver.)
- Overflow (Uncensored)
- Overlord
- Overlord II
- Overlord III
- Overlord IV
- Overlord Movie 1: The Undead King
- Overlord Movie 2: The Dark Hero
- Overlord: Ple Ple Pleiades
- Overlord: Ple Ple Pleiades - Clementine Toubou-hen
- Overlord: Ple Ple Pleiades 2
- Overlord: Ple Ple Pleiades 3
- Overlord: Ple Ple Pleiades 4
- Overlord: The Sacred Kingdom
- Overman King Gainer
- Overtake!
- Owari no Seraph: Vampire Shahar
- Owarimonogatari
- Owarimonogatari Second Season
- Ozanari Dungeon: Kaze no Tou
- Ozma
- Ozmafia!!
