I'm the Hero, But the Demon Lord's Also Me, manga volume 1 features story by Akiyoshi Ota and art by Tatsuya Endo.

Yuuma Tsugari is an ordinary high school student whose family runs a public bath house. He leads a peaceful, uneventful life, but all that changes when a beautiful woman from another world appears before him, certain that he's the hero she's been searching for! Sure, he's no hero, but how can he refuse such a beauty...!?