Anime Series Beginning with O
- [Oshi no ko]
- Curious George
- My Next Life as a Villainess: All Routes Lead to Doom!
- Obey Me!
- Occultic;Nine
- Ochikobore Fruits Tarte
- Octave
- OCTOPATH TRAVELER
- Oda Nobuna no Yabou
- Oda Shinamon Nobunaga
- Odd Taxi
- Odekake Kozame
- Odoru Daisosasen Series
- Oedo Rocket
- Oh! Super MILK Chan
- Oh-oku ( Danjo Gyakuten)
- Oi! Hanimaru
- Oishi Propose
- Oishinbo
- Ojamajo
- Ojarumaru
- Ojisama (warai) Series
- Ojisama Senka
- Ojisan Ha Kawai I Mono Ga Osuki.
- Ojisan to Marshmallow
- Okami Kakushi
- Okami San Ha Taberaretai
- Okami San Ha Taberaretai
- Okami Shojo to Kuro Oji
- Okami to Koshinryo (Wolf and Spice)
- Okane ga Nai!
- Okasan to Issho
- Okiku Furikabutte
- Okitegami Kyoko Series
- Okoshiyasu Chitose Chan
- Okusama ga Seito Kaicho!
- Okusama wa Maho Shojo
- Olympia Cuculus
- Olympic
- Omae Umasodana
- Omae wa mada Gunma wo shiranai
- Omamori Himari
- OMISHI MAGICAL THEATER: RISKY & SAFETY
- Omoi, Omoware, Furi, Furare
- Omoide no Marnie (When Marnie Was There)
- Omukaedesu.
- Oneechan ga Kita
- Onegai My Melody
- Onegai Teacher (Please Teacher!)
- Onegai Twins
- Ongaku Shojo
- Ongaku to Hito
- ONGEKI
- Oni-Chan no Koto Nanka Zenzen Sukijanaindakarane!!
- Onichan Dakedo Ai Sae Areba Kankeinaiyone
- Onigamiden
- Onigiri
- Onihei Hankacho
- Onimai: I'm Now Your Sister!
- Onimusha
- Onipan!
- Onkyokaiwa
- Online Game
- Only Yesterday
- Onna no ko to Misshitsu ni itara XX shichau kamoshirenai.
- Onna no Sono no Hoshi
- Onosaka, Konishi no O+K(OTASUKE)
- Onsen Musume
- Onsen Yosei Hakone-Chan
- Ontama!
- Ookami kodomo no Ame to Yuki (Wolf Children)
- Ookami-san Series
- Ooya-san wa Shishunki !
- Opus.COLORs
- orange
- Ore Ga Sukina No Ha Imotodakedo Imoto Janai
- Ore monogatari!!
- Ore no Imoto ga Kon nani Kawaii wake ga nai
- Ore no Kanojo to Osananajimi ga Shuraba Sugiru
- Ore no nonai sentakushi ga gakuen Love comedy wo Zenryoku de Jyama Shiteiru
- Ore o Suki nano wa Omae dake kayo
- Ore, Twintail ni Narimasu.
- Orenchi no Furo Jijyo
- Oretachi Majikou Destroy
- Oretachin ni Tsubasa wa Nai
- Orient
- Osake wa Fufu ni Nattekara
- Osama Game
- Osama Ranking
- Osananajimi ga zettai ni makenai love-come
- Oshi ga Budokan Ittekuretara Shinu
- Oshigoto Danshi
- Oshiri Tantei
- Osomatsu-san
- Ossan's Love
- Otenki Sentai How Weather
- Otobun
- Otoca Doll
- Otogi Jushi Akazukin
- Otoko wa Tsuraiyo