Are the sexy buttocks not good?

Story :  Ainosuke Hizaki (20 years old) is addicted to anal masturbation, which he started out of curiosity. One day when looking at dating sites on the train to see if someone could make him have an anal orgasm, he gets molested. Seeing something is off, an older handsome man, Okumi, helps him out and let's Ainosuke know that he's good at making guys cum from behind. Though the two don't have "sex", he makes Ainosuke come in a meltingly tender way! Then, however, Ainosuke, slightly dissastified, loses contact with Okumi...?