Sougo Tairitsu Frustration

Oka Kotarou, a regular 17 year old, is quite the player. But the number of times he has come while having sex is a big fat zero. Till one day, he decides to try anal masturbation. But suddenly, his childhood friend Murashige walks in while Kota is in the middle of his experiment. And what's more, Murashige offers to help...?!