| Onmyō Taisenki | September 30, 2004 | — | 52 |
| Onna no Ko tte | February 5, 2015 | — | 4 |
| Onsen Yōsei Hakone-chan | October 4, 2015 | — | 13 |
| Onyankopon | October 6, 2017 | — | — |
| Ooya-san wa Shishunki! | January 10, 2016 | — | 12 |
| Operation Han-Gyaku-Sei Million Arthur | October 25, 2018 | — | 24 |
| Opus Colors | April 7, 2023 | — | 12 |
| Orange | July 3, 2016 | Tokyo MX | 13 |
| Orb: On the Movements of the Earth | October 5, 2024 | NHK General TV | 25 |
| Ore to Yu Nii! | — | — | — |
| Ore wa Chokkaku | January 5, 1991 | — | 36 |
| Ore wa Teppei | September 12, 1977 | — | 28 |
| Ore, Tsushima | July 3, 2021 | — | 12 |
| Oreimo | February 22, 2011 | — | 4 |
| Oreimo | October 3, 2010 | — | — |
| Oreshura | January 6, 2013 | — | 13 |
| Oresuki | October 3, 2019 | — | — |
| Oretachi Ijiwaru-kei | December 26, 2004 | — | 14 |
| Orient | January 6, 2022 | — | 24 |
| Oruchuban Ebichu | August 1, 1999 | — | 12 |
| Osake ni Yowai Andō-san | — | — | — |
| Osamake | April 14, 2021 | — | 12 |
| Oshare ni Naritai! Peanuts-kun | — | — | — |
| Oshi no Ko | April 12, 2023 | — | 35 |
| Oshiri Kajiri Mushi | October 7, 2012 | NHK BS Premium | — |
| Osomatsu-kun | February 5, 1966 | — | 56 |
| Osomatsu-kun | February 13, 1988 | — | 86 |
| Otaku Elf | April 8, 2023 | — | 12 |
| Otaku Vampire's Love Bite | — | — | — |
| Otanoshimi Anime Gekijō | April 5, 1970 | — | 26 |
| Otenba Lulu | — | — | — |
| Otherside Picnic | January 4, 2021 | — | 12 |
| Otherworldly Munchkin | — | — | — |
| Otogi Manga Calendar | May 1, 1961 | — | — |
| Otogi Zoshi | July 6, 2004 | Nippon Television | 26 |
| Otogi-Jūshi Akazukin | July 1, 2006 | — | — |
| Otoko Ippiki Gaki Daishō | September 29, 1969 | — | 156 |
| Otome wa Boku ni Koishiteru | October 8, 2006 | — | 12 |
| Otome wa Boku ni Koishiteru: Futari no Elder | — | — | 3 |
| Otome Yōkai Zakuro | October 5, 2010 | TV Tokyo | 13 |
| Otona nya Koi no Shikata ga Wakaranē! | October 5, 2020 | — | 8 |
| Our Home's Fox Deity | April 6, 2008 | — | 24 |
| Our Last Crusade or the Rise of a New World | October 7, 2020 | — | 12 |
| Ouran High School Host Club | April 5, 2006 | Nippon Television | 26 |
| Outbreak Company | October 3, 2013 | — | 12 |
| Outlaw Star | January 9, 1998 | — | 26 |
| Over Drive | April 4, 2007 | — | 26 |
| Over Drive Girl 1/6 | April 6, 2019 | — | — |
| Overflow | — | — | 8 |
| Overgeared | October 2, 2026 | — | — |
| Overlord | July 7, 2015 | AT-X | 52 |
| Overman King Gainer | September 7, 2002 | — | 26 |
| Overtake! | October 1, 2023 | — | 12 |
| Ox Tales | April 7, 1987 | TV Tokyo | 101 |
| Oyako Club | October 3, 1994 | — | — |
| Ozanari Dungeon: Kaze no Tō | September 27, 1991 | — | — |
| Ozmafia!! | July 7, 2016 | — | 12 |
| Ozuma | March 16, 2012 | — | 6 |
| Paboo & Mojies | May 5, 2012 | — | — |
| Pan de Peace! | April 4, 2016 | — | 13 |