Novel & Essay Series Beginning with O
- My Next Life as a Villainess: All Routes Lead to Doom!
- Ochoyan
- Odd Taxi
- Odekake Kozame
- Odoru Daisosasen Series
- Oh! My Girl!!
- Ohoka Echizen
- Oishi Propose
- Oishii Coffee no Irekata
- Oishii Gohan
- Oishinbo
- Ojamajo
- Ojarumaru
- Ojiisan Sensei
- Ojisan to Marshmallow
- Okami Shojo to Kuro Oji
- Okane ga Nai!
- Okitegami Kyoko Series
- Omoi, Omoware, Furi, Furare
- Omoide no Marnie (When Marnie Was There)
- Omoshiro Nankyoku Ryorinin
- Once Upon a Time in High School
- One Piece
- One Punch Man
- Onegai My Melody
- Ongaku to Hito
- Ongaku-shi ga Kakanai Jpop Hihyo
- Onigamiden
- Onigiri
- Onihei Hankacho
- Onimusha
- Oniyome Nikki
- Online Game
- Only Yesterday
- Onna Joshu Naotora
- Onna Kudoki Meshi
- Onna wa sore wo yurusanai
- Onsen Musume
- Ookami kodomo no Ame to Yuki (Wolf Children)
- Opanchu Usagi
- orange
- Ore monogatari!!
- Ore no Sora Series
- Ore, Tsushima
- Orient
- Orix Buffaloes
- Orthros no Inu
- Osama Game
- Osama Ranking
- Osen
- Oshiri Tantei
- Osomatsu-san
- Osozaki no Himawari
- Otaku ni Koi wa Muzukashii
- Otherside PIcnic
- Otoko wa Tsuraiyo
- Otokomeshi
- Otokotachi no Yamato
- Otome wa Boku ni Koishiteru
- Otome Yokai Zakuro
- Otome-San
- Otona Anime
- Otona Joshi
- Otona No Nurie
- Otoyome Gatari
- Ougon no Gt
- OUR HOUSE
- Ouroboros
- Outbreak Company
- Outlandar
- Overlord
- Seraph of the End