Masuda Ayumu

The main character.
He is a shy and timid boy. On his way home from school, he is mugged by a delinquent and dragged into a back alley, where he is rescued by a magical girl named Yuri. However, when Yuri's magic fails, he laughs, which causes her displeasure, so she casts a spell on him that makes him unable to stop ejaculating.