HUNTB-104 (You Helped Me Study, So I'll Teach You Naughty Things) A Private Lesson With Strings Attached Between My Step-Sister, A Whore Whose Grades Are Dropping Like A Rock, And Me, A Virgin And A Nerd

One day, my sister-in-law, who hadn't studied at all, suddenly said, "I'm going to college!" At the request of her mother-in-law, I decided to teach her, but... This is impossible! I can't do it! I give up on my sister-in-law who is too stupid as soon as possible. However, my sister-in-law says that if she teaches me to study, I will teach her naughty things. I'm a hard worker and good at studying, and my sister-in-law is a bimbo, so she's good at sex. Result…A win-win equivalent exchange was established! Start a secret private lesson!