| Ogenki Clinic | July 20, 1991 | — | 3 |
| Ogre Slayer | September 9, 1994 | — | 4 |
| Oh Boy, Was I Wrong About Her | July 6, 2026 | — | 12 |
| Oh My Goddess! | — | — | 5 |
| Oh My Goddess! | January 6, 2005 | TBS Television | — |
| Oh My Goddess! | February 23, 2011 | — | 3 |
| Oh! Edo Rocket | April 3, 2007 | — | 26 |
| Oh! Family | October 6, 1986 | TV Tokyo | 26 |
| Oh! My Goddess: The Adventures of Mini-Goddess | April 6, 1998 | — | — |
| Ohayou Hakushon Daimaou | — | — | 237 |
| Ohayō! Spank | March 7, 1981 | — | 66 |
| Ohayō! Unko-sensei | July 26, 2024 | — | — |
| Oi! Ryoma | April 7, 1992 | NHK General TV | 39 |
| Oishinbo | October 17, 1988 | — | 136 |
| Ojamajo Doremi | February 7, 1999 | — | 201 |
| Ojamajo Doremi: Owarai Gekijō | March 23, 2019 | — | 26 |
| Ojamanga Yamada-kun | September 28, 1980 | — | 101 |
| Ojarumaru | October 5, 1998 | NHK Educational TV | 1,868 |
| Ojisan and Marshmallow | January 7, 2016 | — | 12 |
| Okama Report | March 12, 1991 | — | 3 |
| Okami-san and Her Seven Companions | July 1, 2010 | — | 12 |
| Okawari-Boy Starzan S | January 7, 1984 | Fuji Television | 34 |
| Okitsura | January 5, 2025 | — | 12 |
| Okojo-san | October 2, 2001 | TV Tokyo | 51 |
| Oku-sama wa Joshi Kōsei | July 2, 2005 | Television Kanagawa | 13 |
| Oku-sama wa Mahō Shōjo: Bewitched Agnes | July 3, 2005 | — | 13 |
| Omae wa Mada Gunma o Shiranai: Reiwa-ban | January 10, 2026 | — | 12 |
| Omae, Tanuki ni Naranee ka? | — | — | — |
| Omakase Scrappers | April 7, 1994 | NHK Satellite 2 Television | — |
| Omakase! Miracle Cat-dan | March 31, 2015 | NHK Educational TV | 32 |
| Omamori Himari | January 6, 2010 | — | 12 |
| Omishi Magical Theater: Risky Safety | October 5, 1999 | WOWOW | 24 |
| Omniscient Reader's Viewpoint | — | — | — |
| On Air Dekinai! | January 10, 2022 | — | 12 |
| Onaji Semi no Someya-san ga Sexy Joyū datta Hanashi | July 5, 2026 | — | — |
| Once Upon a Time... Man | 1978 | France Régions 3 | 26 |
| Once Upon a Time... Space | October 2, 1982 | France Régions 3 | 26 |
| Once Upon a Witch's Death | April 1, 2025 | — | 12 |
| One Outs | October 8, 2008 | — | 25 |
| One Piece | December 12, 1999 | Fuji Television | 1,169 |
| One Room | January 11, 2017 | — | — |
| One Week Friends | April 6, 2014 | Tokyo MX, AT-X, Nippon BS Broadcasting, TV Aichi, MBS, ANIPLUS | 12 |
| One-Punch Man | October 4, 2015 | TX Network | 24 |
| One: Kagayaku Kisetsu e | August 10, 2001 | — | 4 |
| Oneechan ga Kita | January 8, 2014 | — | 12 |
| Onegai AiPri | April 5, 2026 | — | — |
| Onegai My Melody | April 3, 2005 | — | — |
| Onegai My Melody Kirara | April 6, 2008 | — | 52 |
| Onegai My Melody: Kuru Kuru Shuffle | April 3, 2005 | TX Network | — |
| Onegai! Samia-don | April 2, 1985 | NHK General TV | 78 |
| Ongaku Shōjo | July 6, 2018 | — | 12 |
| Oni Chichi | October 30, 2009 | — | 2 |
| Oni Chichi 2 | October 29, 2010 | — | 2 |
| Oni: Thunder God's Tale | October 21, 2022 | — | 4 |
| Oniichan dakedo Ai sae Areba Kankeinai yo ne! | October 5, 2012 | AT-X | 12 |
| Onimai | January 5, 2023 | — | 12 |
| Onipan! | April 11, 2022 | TX Network | 12 |
| Only You: Viva! Cabaret Club | — | — | — |
| Onmyo Kaiten Re:Birth Verse | July 3, 2025 | — | 12 |
| Onmyoji | November 28, 2023 | — | 13 |