| Omegaverse IRL?! | 2025-11-05 | - |
| Omegane Teacher -Valentine Plan- | 2003-02-14 | - (1) |
| Omega no Shikai -Miyo Owareru Shimai Towa(●nd)- | 2010-08-14 | 7.40 (16) |
| Omega no Shikai -Aki Kaketa Shiki no Ai: Zan- | 2009-08-15 | 7.40 (14) |
| Omega no Shikai -Aki Kaketa Shiki no Ai- | 2008-08-17 | 6.90 (19) |
| Omega no Shikai -1. Shiki no Hajimari- | 2006-12-31 | 6.90 (22) |
| Omega Vampire | 2016-12-02 | 7.40 (128) |
| Omawari-san: Koitsu Desu. | 2017-07-09 | - (3) |
| Omatsuri no Yoru ni | 2022-11-04 | - (2) |
| Omatsuri Yarou | 2014-08-17 | - (3) |
| Omatase! Instant ~Anata wa Dare o Meshiagaru?~ | 2009-09-11 | 6.20 (11) |
| Omata Yurume wa Mama Naranai | 2016-12-31 | - (1) |
| Omase na Princess ~Miwaku no Lolicon Nikubenki-tachi~ | 2013-04-30 | 6.20 (19) |
| Omana 2: Omaenchi Moeteruzo | 2006-02-24 | - (1) |
| Omamori: A MP100 Fangame | - | - |
| Omamagoto ~Himitsu no Oyuugi, Mama ni wa Naisho~ | 2005-07-29 | - (3) |
| Omamagoto ~Hahaoya Shoujo to Chiyahoya Shippori~ | 2017-06-30 | 6.00 (28) |
| Omakase☆Demakase Angel!! ~Chocolat to Milfy Shukufuku Shichau zo~ | 2000-09-01 | - (2) |
| Omakase! Obenkyou☆Sisters | 2009-08-28 | 6.40 (11) |
| Omae wa Juujin Niku Benki ~Tanezuke Mugen Loop~ | 2013-03-29 | 5.80 (46) |
| Omae no Tsuma wa, Ore no Inran Niku Yome ~Otonari-san wa Yokkyuu Fuman Deshita~ | 2017-02-03 | 6.00 (11) |
| Omae no Pantsu wa Nani-iro da!? | 2011-12-22 | 6.70 (47) |
| Omae no Onna o Netotteyaru ~Mukashi Yatta Onna wa Ima wa Hakui no Tenshi. Danna no Mae de Kokoro mo Shintai mo Moteasonde Netoru~ | 2012-12-21 | 6.80 (37) |
| Omae no Novel Game ga Kansei Shinai Riyuu 2 | 2025-12-31 | - (2) |
| Omae no Natsuyasumi | 2004-03-26 | 6.10 (6) |
| Omae no Mono wa Ore no Mono ~Otto ni wa Misenai Midara na Kao o Otouto ni Sarasu Kyonyuu Wakazuma~ | 2012-08-24 | 7.20 (131) |
| Omae no Mono wa Ore no Mono | 2004-11-26 | - (3) |
| Omae no Mama o Share Shiyou ze ~Musuko e no Ijimekko-tachi ni Otosareru Bibo~ | 2016-03-04 | 6.40 (48) |
| Omae no Kaa-chan, Mesu Buta Niku Benki ni Nattenzo? | 2011-12-04 | 5.70 (11) |
| Omae no Kaa-chan, Ii Onna Da yo na. | 2018-09-21 | 7.50 (285) |
| Omae no Danna Datte Ore no Tsuma o Ubattan Dakara, Ii Darou? ~Fukushuu no Netori~ | 2016-07-01 | 6.30 (39) |
| Omae ga Motetaitte Iu kara Daro!! Okawari (1) | 2021-01-05 | - |
| Omae ga Motetaitte Iu kara Daro!! | 2020-09-07 | - |
| OmOneko | 2025-03-03 | 7.30 (15) |
| Olympus Rising: Ragnarok | 2026-03-27 | - |
| Olympus Rising | 2025-08-01 | - |
| Olympia Soiree Catharsis | 2025-12-18 | 6.90 (23) |
| Olympia Soiree | 2020-04-16 | 7.80 (722) |
| Olli: Neozhidannoe puteshestvie | 2016-01-04 | - (2) |
| Olivine Lights | 2024-01-10 | 6.70 (6) |
| Olivia's Bad Day | 2023-06-07 | - (2) |
| Olivia Dwight | - | - |
| Oliver Renhelf | 2017-04-13 | 5.40 (5) |
| Olga Mania | 2008-08-22 | - |
| Olga Doesn't Die | 2026-01-30 | - (3) |
| Old-Timer | 2010-08-14 | 6.20 (5) |
| Old Web Cobwebs | 2023-07-25 | - (2) |
| Old Story | - | - (4) |
| Old Software | - | 5.50 (6) |
| Old Gay Cats Look at Old Photos | - | - (1) |