Muromi-san

The short anime Muromi-san is based on the manga of the same name and from what I can tell seems to be a slapstick and/or absurdist situational comedy centering around the relationship between Muromi-san, the mermaid of the title, and a human boy named Takuro Mukojima.

Muromi-san is enthralled by Takuro, who gets sucked into her shenanigans because she's a quirky one, and more than she seems. She's not the only creature to cross paths with Takuro either, as there are many others in the world and Takuro learns about them as he goes.