There are nights where they just sip sake and cuddle up beside each other.
That's just the polite way of saying it.
Said nights usually involve scary drinking competitions, with both getting wildly drunk.
They then proceed to scare the shit outta Ganjyuu by having hot sex in the middle of the living room.
Ganjyuu has many a time sworn never to reveal their secret on pain of a long, excruciating death.