Similar to 押忍!!空手部

I'm the Evil Lord of an Intergalactic Empire!

Oresuki

Merman in My Tub

The Foolish Angel Dances with the Devil

Seraph of the End

On Air Dekinai!

On-Gaku: Our Sound

Ongaku Shōjo

Music Land

Noiseman Sound Insect

Onsen Yōsei Hakone-chan

On-chan

Onna no Sono no Hoshi

Onmyōji (literary series)

Onmyō Taisenki