When they were little Eiko and Haruka liked to play superhero, although Eiko was better at it. But then Eiko had to move away, and they promised each other that they would keep on being superheroes. Now Haruka is in high school and is a fairly ordinary girl, and Eiko has moved back – and kept up her end of the bargain.
(Source: Natsuyume)

The manga is a romantic comedy starring the clever and handsome son of a wealthy family. In middle school he only ever studied, and everyone said he was plain like a background character. When he gets to high school, he enacts a plan to change his image to be more like a "main character" and get the perfect girlfriend.

The story revolves around Haruki and his four sisters: Mutsuki, Yayoi, Uzuki, and Satsuki. While their life may seem monotonous—aside from the fact that Haruki's sisters don't give him a single opportunity to rest, lecturing him about every perceived mistake and playing tricks on him—Haruki still likes his life.

(Source: MAL News)