Bittersweet Sin (Nijimura Shuzo Tribute)

Keiko Nijimura and Shuzo Nijimura are known to be very close siblings but not many people (only the two of them) know their true relationship. They both have an extremely high fetishes for each other leading to a sexual and romantic liason.

They were living very peacefully until Keiko's male teacher came in the picture. Kyosen Sei, or his collegues and students call him Sensei, was very curious with Keiko since she was the only one not attracted to him. Being a major pervert he is, he tried lots of ways to get Keiko fall for him including sexual contact.

Then add her best friend, Shougo Haizaki, who was falling in love with her because they were together since middle school. He knows that she knows he was a playboy and doesn't know how to approach her about it. He's also afraid of her brother where he remembers that he's been beaten up by him a few times. When he saw Sensei and her doing it taking advantage of her trauma he finally does it.

With Shuzo having sex with his younger sister, Keiko with the both of them, Haizaki taking advantage of her fear and Sensei doing it with his student. How will they ever part with their bittersweet sin.