From Chibi Manga:

"I fell in love with Sensei"
Risa loves basketball and is a captain of a small weak basketball club. One day she got lost into a cram school called karakusa terako and met a soft haired mizuno sensei.

Sensei encouraged her to pursue her dream into a high school with strong basketball team. Even though she knows that he is a teacher, and has a girlfriend, when she realized, sensei has occupied her heart.