Mezamereba Ningyo Hime

Mezamereba Ningyo Hime (めざめれば人魚姫, lit. "The Awoken Mermaid Princess") is a manga series by Natsumi MAtsumoto.

Plot
A collection of four short stories. The main one is about a girl named Nanami, the boy she likes named Takeru, and a strange girl in their class who befriends Nanami and reveals startling news about Nanami’s past and her true heritage. The second story is about a girl who discovers there is a catboy in her class at school! Finally, the last two stories are about the adventures of some tiny trouble-making demons.