Natsume's Book of Friends, Volume 5 by Yuki Midorikawa

Takashi Natsume has always been aware of the supernatural world, but after he inherits a magical book from his grandmother, the supernatural world is aware of him!

Takashi Natsume can see the spirits and demons that hide from the rest of humanity. He has always been set apart from other people because of his gift, drifting from relative to relative, never fitting in. Now he's a troubled high school student who has come to live in the small town where his grandmother grew up. And there he discovers that he has inherited more than just the Sight from the mysterious Reiko.

Takashi thinks he's found a balance between yokai and friends when he goes with a group of classmates to a country inn for a marathon cram session before school starts again. But even the prosaic threat of homework can't keep the ""other world"" at bay, especially when the innkeeper has been dabbling in mermaid blood!