Tsuyokiss

Tsuyokiss is about the lives of a group of high school students and the often comedic events that occur around them.

The protagonist is an ordinary boy named Leo Tsushima. He is secretly in love with the eldest daughter of the Kiriya Corporation, Erika Kiriya, who is also the student council president.

One day, a senior female student, Otome Kurogane, knocks out several of the main characters when they were trying to sneak into school being late. Surprisingly, it turns out that she is Leo’s beloved cousin that he had not seen for years. And she decides to move in to the same house with Leo, whose mediocre life starts to change into something a lot more exciting.

[Edited from Wikipedia]