It's about these twins where the other one is in a school of delinquents and he often sleep around with other men and he's muscular as well. Then he got into an accident and was hospitalized so his twin (MC, he's slim unlike his twin) took his place and he's often being asked for sex, and this is where he meets this short seme. They also feel it when the other is aroused and this muscular twin is really obsessed with the slim twin because of pleasure.
Sasuga Kim Seojun! Always know your priorities no matter who it is. (づ ̄ ³ ̄)づ