Responses
It won't happen. The pairs, particularly the main one is fiercely loyal to each other, well it's Cain whose very fiercely loyal and possessive to his partner.
However, there is actually a special chapter which is non canon where a threesome happens. There's sadly no penis penetration though but still, it's very hot. The uke there was veeery lucky.
Damn... Dats a big loss. （￣へ￣）
I pray for threesome. God please. (▰˘◡˘▰)