He is the ghost of a man Madoka once described as her only family and is heavily implied the two were in love. He was killed when the cave he was in collapsed killing him and several students engaged in sexual behavior.
His spirit returned full of regret and lost his memory. Because of his time in the cave and his memory loss, he believed he existed to act as a rapist and attacked several students. Madoka caught him and as he began violating her, memories returned to him causing him temporary remorse and pain. When Madoka catches him in the act again, Asahina rapes Madoka and threatens her friend, Sayako who hated him. Madoka keeps allowing Asahina to violate her but Asahina has a large amount of stamina and recovers frequently.
Sayako soon sees her friend with Asahina and secretly offers to take Madoka's place. While he does violate Sayako, Asahina only thinks of Madoka. Madoka soon sees Asahina with Sayako and slaps him. Soon Asahina regains his memories and slowly shows remorse for his actions. Madoka then makes Asahina realize he has no reason to be bound on Earth anymore. Asahina begins to cross over, but not before he realized all he ever needed was Madoka.