Shinshoku

The protagonist, Kokubo Toshiya, is adopted by the loving Kitagawa family. In truth, he was in cahoots with the orphanage's director, and aimed to turn the women of this family into his prey.

Despite conducting himself as a mature and overly polite child, Kokubo Toshiya secretly harbors dark thoughts, this twisted personality being a result of a traumatic childhood experience.

Gradually, he starts to show his true personality just before starting his plans on his stepmother and stepsister.

While his stepfather is away from home, Toshiya starts putting his plan in practice. Using a photo of his stepsister shoplifting, he starts with her stepmother, and soon he also reaches his hand on his stepsister.