The protagonist, Yuta, meets again with Rima, an old friend of his who has run away from home and crashes into his bedroom.
She is completely careless and her panties are showing. After she falls asleep, Yuta, who is a hopeless virgin, gets extremely curious.
He then decides to introduce his penis in her butt, and that felt so good that he ends up giving her an accidental creampie.
After that, things escalate fast.