I think it refers to the Kdrama “ S lines” a red string represents how many times the person had sex and if they had a red string that connects both of them that means they slept together… so in this case this is ian’s first time and its with eunsan while eunsan has slept with multiples
Yuta seems addicted to this pill. Maybe he needs it to prepare himself from going insane, or maybe a muscular relax pill to feel less when engaging with intimacy or maybe even to make his manhood hard?....
That was just... lovely.