The proper way of drinking sake on a woman is by pouring it on her boobs and vagina. Meanwhile, the way to drink to it on a man is to pour the sake on the penis and suck on it.
Gangchan wants to learn some workout exercises from Seyoung but that takes a weird direction. She then pounces on him while he was still asleep. Gangchan wakes up to Seyoung being on top of him, and then SHE FUCKS THE SHIT OUTTA HIM.