Ruka became Dai's new mother after the divorce. However, Ruka is a studious mother and Dai is forced to study every day, so he consults with his bad classmate Masa... One day, Masa lies and says, "Dai forces me to cheat every day." Shocked, he has no choice but to listen to Masa's words to protect Dai, knowing that if the school finds out, it will be a big problem, and he ends up groping her big breasts and even having sex with her... Dai secretly records the evidence and blackmails his stepmother for revenge!