Light 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
- Oishii Coffee no Irekata
- Ojamajo
- Okami Kakushi
- Okami Shojo to Kuro Oji
- Okami to Koshinryo (Wolf and Spice)
- Okane ga Nai!
- Okitegami Kyoko Series
- Omamori Himari
- Once Upon a Witch's Death
- One Piece
- Onegai My Melody
- Onegai Teacher (Please Teacher!)
- Onegai Twins
- Onichan Dakedo Ai Sae Areba Kankeinaiyone
- Onimusha
- Oniyome Nikki
- Online Game
- Ontama!
- Ookami kodomo no Ame to Yuki (Wolf Children)
- Ookami-san Series
- Ore Ga Sukina No Ha Imotodakedo Imoto Janai
- Ore ha Subete wo <Parry> suru
- 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.
- Osananajimi ga zettai ni makenai love-come
- Osomatsu-san
- Otogi Jushi Akazukin
- Otome wa Boku ni Koishiteru
- Outbreak Company
- Overlord
- OZMAFIA!!
- Seraph of the End
- Shomin Sample