The Teacher is a young man wearing glasses with light-colored hair and eyes. He is wearing a white collared shirt over a dark vest with slacks. He sports a watch on his left wrist and is wearing tennis shoes.
The Teacher initially seem to be a sympathetic man who cares for his students. However, he has a much darker side to him where he makes unwanted advances on his students, in particular Sachiko Shinozaki. His true self is a brash man who openly humiliates and shames his pupils.
One rainy day, after-school, when Sachiko was looking out the window from the third floor hallway, her teacher saw her from the second floor and meets up with her. He makes small chit-chat, asking how is she doing. The Teacher then pulls her in initially for a kiss before he starts to molest her. Sachiko tries to push him away, but he starts to strip away her clothing.
Sachiko threatens her teacher, stating that she will tell everyone about this incident which would eventually make him lose his teaching license. The Teacher in response mocks her, asking who would even listen to an outcast like her. In despair, Sachiko climbs up the railing of the hallway and warns him that she will jump to her death. The Teacher had enough of her theatrics and grabs her arm, however it causes her to lose her footing and she falls to her death.
In shock, the Teacher tries to conceal her body and is discovered by the Principal. The Principal, who didn't want to tarnish the name of his school, helped him bury her body in the basement of their school. Even after Sachiko's death, the Principal and the Teacher still visit her grave to desecrate her body.
Sachiko's mother, Yoshie Shinozaki, never gave up looking for daughter and it is shown she still questions the Teacher about her disappearance. However, the Teacher kept giving her excuses, much to Yoshie's dismay. In the end, Sachiko was trapped inside the school where she curses the Teacher whose fate is left unknown.
Significant plot details end here.
In the picture that was found by Yoshiki Kishinuma and Ayumi Shinozaki the Teacher can be seen sitting next to Sachiko. His face is also crossed over, meaning he died inside of the school, although the manga never discloses how he died.