Paperback, Novel Series Beginning with O
- [Oshi no ko]
- My Next Life as a Villainess: All Routes Lead to Doom!
- Occultic;Nine
- OCTOPATH TRAVELER
- Oda Nobuna no Yabou
- Odd Taxi
- Odoru Daisosasen Series
- Oh! My Girl!!
- Ohoka Echizen
- Oishi Propose
- Oishii Coffee no Irekata
- Oishinbo
- Ojamajo
- Okami Kakushi
- Okami Shojo to Kuro Oji
- Okami to Koshinryo (Wolf and Spice)
- Okane ga Nai!
- Okitegami Kyoko Series
- Omamori Himari
- Omiyasan
- Omoi, Omoware, Furi, Furare
- Omoide no Marnie (When Marnie Was There)
- Omoshiro Nankyoku Ryorinin
- Omukaedesu.
- One Piece
- Onegai My Melody
- Onegai Teacher (Please Teacher!)
- Onegai Twins
- Ongaku to Hito
- Ongaku-shi ga Kakanai Jpop Hihyo
- Onichan Dakedo Ai Sae Areba Kankeinaiyone
- Onigamiden
- Onigiri
- Onihei Hankacho
- Onimusha
- Oniyome Nikki
- Online Game
- Only Yesterday
- Onna wa sore wo yurusanai
- Ontama!
- Ookami kodomo no Ame to Yuki (Wolf Children)
- Ookami-san Series
- 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 no Sora Series
- Ore o Suki nano wa Omae dake kayo
- Ore, Twintail ni Narimasu.
- Orient
- Orthros no Inu
- Osama Game
- Osama Ranking
- Osananajimi ga zettai ni makenai love-come
- Osen
- Oshiri Tantei
- Osomatsu-san
- Otherside PIcnic
- Otogi Jushi Akazukin
- Otoko wa Tsuraiyo
- Otokomeshi
- Otokotachi no Yamato
- Otome wa Boku ni Koishiteru
- Otome Yokai Zakuro
- Otome-San
- OUR HOUSE
- Ouroboros
- Outbreak Company
- Outlandar
- OZMAFIA!!
- Seraph of the End
- Shomin Sample