From Mintwood Scans:
Maki confessed to his best friend Katsumi, but was told he was “disgusting”.
They are coincidentally reunited after 10 years apart. Although their reunion should be a joyous one, Maki discovered that the once straight man is now sleeping with men who have dangerous reputations.
Little did he know, after once being assaulted, Katsumi began to have violent sex to punishing himself for hurting Maki in his terrible self-protection.
In response to those feelings, Maki says, “Katsumi-kun, I will punish you.”