Similar to 穏やか貴族の休暇のすすめ。

Oi! Ryoma

Oh! Edo Rocket

Ōoku: The Inner Chambers

Ōkami Kakushi

Wolf Children

Wolf Girl and Black Prince

Wolf Boy Ken

Super Milk Chan

Over Drive (manga)

Overman King Gainer

Over Rev!

Kaina of the Great Snow Sea

All Out!!

My Wife Is the Student Council President

Oku-sama wa Joshi Kōsei

Oku-sama wa Mahō Shōjo: Bewitched Agnes

Ogenki Clinic

Okoshiyasu, Chitose-chan

Fish in the Trap