Based on the manga by Miyabi Tsuzuru.
https://www.traditionrolex.com/13
Kazuhiko has a big crush on his stepmother, or rather, he wants to have sex with her. Since he can't just ask it from her directly nor force it on her, he comes up with quite a devious plan, step by step leading him closer to his goal. But in the end, his stepmother won't be enough for him...