Games Series Beginning with O
- [Oshi no ko]
- My Next Life as a Villainess: All Routes Lead to Doom!
- Obey Me!
- Occultic;Nine
- Octave
- OCTOPATH TRAVELER
- Oda Nobuna no Yabou
- Odoru Daisosasen Series
- Oishinbo
- Ojarumaru
- Ojisama Senka
- Okami Kakushi
- Okami to Koshinryo (Wolf and Spice)
- Okasan to Issho
- Okiku Furikabutte
- One Piece
- One Punch Man
- One Room
- Onegai My Melody
- Ongaku Shojo
- Ongaku to Hito
- ONGEKI
- Onigiri
- Onimai: I'm Now Your Sister!
- Onimusha
- Online Game
- Onna no ko to Misshitsu ni itara XX shichau kamoshirenai.
- Onsen Musume
- Opus.COLORs
- Ore no Imoto ga Kon nani Kawaii wake ga nai
- Ore no Kanojo to Osananajimi ga Shuraba Sugiru
- Oretachi Majikou Destroy
- Oretachin ni Tsubasa wa Nai
- Orient
- Osama Ranking
- Osananajimi ga zettai ni makenai love-come
- Oshi ga Budokan Ittekuretara Shinu
- Oshiri Tantei
- Osomatsu-san
- Otoca Doll
- Otogi Jushi Akazukin
- Otoko wa Tsuraiyo
- Otome continue
- Otome wa Boku ni Koishiteru
- otona MUSE
- Ouran Koko Host Club
- Outbreak Company
- Overlord
- OZMAFIA!!
- Ozuma
- Seraph of the End
- The Royal Tutor (Oshitsu Kyoshi Haine)