From SMM :

A girls' high school that Mamoru attends has amalgamated a boys' high school, which was her wish for a long time. She expects that she will be able to find a boyfriend soon. However, boy students are around ten percent of girl students, and Mamoru is annoyed because her classmate Azuma makes a pass at her. He is known to be dirty-minded. When she was fighting against him as usual, he kissed her all of a sudden.