Karamaru Himono Akai Ato

Karamaru Himono Akai Ato summary:

On the surface, Asai is your picture-perfect "normal" high school student. However, he has always pretended not to notice the burning desire he harbors deep inside him... that is, the intense excitement he feels from seeing someone tied up in red ropes and the marks they leave behind on their pale skin. One day, Asai reluctantly delivers a printout to his classmate, Rui, who is rumored to be the son of a gang member. When he peers inside Rui's home from the open cracks of his door... he finds his classmate bound in red ropes as a man caresses his bare body...
A sweet and exquisitely sensual Yaoi about a sadistic nice guy and a seductive son of a gang member who sells his body for money, both caught in a whirlwind of dilemma!