| OG Divine Wars | Mecha,Sci-fi | 25 |
| Ojamajo Doremi | Comedy,Magic,Shoujo | 51 |
| Okane Ga Nai | Drama,Romance,Shounen Ai,Yaoi | 4 |
| Okusama Wa Joshikousei (2005) | Comedy,Drama,Ecchi,Romance,School Life,Seinen,Slice of Life | 13 |
| Okusama Wa Mahou Shoujo | Comedy,Ecchi,Magic,Romance | 13 |
| Old-Lady Spoon | Magic | 130 |
| Omamori Himari | Action,Comedy,Ecchi,Harem,Romance,Supernatural | 12 |
| On Your Mark | Action,Adventure,Drama,Fantasy,Military,Romance,Sci-fi,Slice of Life,Supernatural | 1 |
| One Outs | Action,Psychological,Seinen,Sports | 25 |
| One Piece (2000) | Adventure,Comedy,Fantasy,Shounen | 1 |
| One Piece: Chinjuujima No Chopper Oukoku | Adventure,Comedy,Fantasy,Shounen | 1 |
| One Piece: Dead End No Bouken | Adventure,Comedy,Fantasy,Shounen | 1 |
| One Piece: Episode Of Arabasta - Sabaku No Oujo To Kaizoku-Tachi | Action,Adventure,Comedy,Shounen | 2 |
| One Piece: Episode Of Chopper Plus - Fuyu Ni Saku, Kiseki No Sakura | Action,Adventure,Comedy,Fantasy,Shounen | 2 |
| One Piece: Karakurijou No Mecha Kyohei | Adventure,Comedy,Fantasy,Shounen | 1 |
| One Piece: Nejimaki Jima No Bouken | Adventure,Comedy,Fantasy,Shounen | 1 |
| One Piece: Norowareta Seiken | Adventure,Comedy,Fantasy,Shounen | 1 |
| One Piece: Omatsuri Danshaku To Himitsu No Shima | Adventure,Comedy,Fantasy,Shounen | 1 |
| One Piece | Action,Adventure,Comedy,Drama | 481 |
| Onegai My Melody | Fantasy,Magic | 52 |
| Onegai Teacher | Comedy,Drama,Romance,Sci-fi | 13 |
| Onegai Twins | Comedy,Drama,Romance,Sci-fi | 13 |
| Onegai My Melody: Kuru Kuru Shuffle! | Comedy,Fantasy | 52 |
| Onii-chan No Koto Nanka Zenzen Suki Janain Dakara Ne ! ! | Comedy,Ecchi,Romance | 12 |
| Only Yesterday | Drama,Romance,Slice of Life | 1 |
| Onmyou Tai Senki | Action,Adventure,Fantasy,Supernatural | 52 |
| Ontama! | Adventure,Magic | 5 |
| Ookami Kakushi | Action,Drama,Horror,Mystery,Psychological,Supernatural | 12 |
| Ookami-San To Shichinin No Nakama-Tachi | Comedy,Romance | 12 |
| Ookiku Furikabutte: Natsu No Taikai-Hen | Comedy,Sports | 13 |
| Ookiku Furikabutte | School Life,Sports | 26 |
| Ore No Imouto Ga Konna Ni Kawaii Wake Ga Nai | Comedy,Drama,Seinen | 12 |
| Origin- Spirit Of The Past | Adventure,Drama,Fantasy,Romance,Sci-fi | 1 |
| Orphen The Revenge | Adventure,Comedy,Fantasy,Magic,Shounen | 23 |
| Orphen | Action,Adventure,Comedy,Fantasy,Magic | 24 |
| Otogi Zoushi | Adventure,Drama,Fantasy,Historical | 26 |
| Otome Youkai Zakuro | Historical,Supernatural | 13 |
| Otome Wa Boku No Koishiteru | Comedy,Drama,Romance,School Life,Shoujo Ai | 12 |
| Ouran High School Host Club | Comedy,Drama,Romance,School Life,Shoujo,Slice of Life | 26 |
| Outlanders | Action,Adventure,Comedy,Ecchi,Fantasy,Martial Arts,Romance,Sci-fi,Seinen,Space,Supernatural | 1 |
| Outlaw Star | Adventure,Comedy,Drama,Ecchi,Mecha,Romance,Sci-fi,Space | 26 |
| Overdrive | Comedy,School Life,Shounen,Sports | 26 |
