You were returning from a visit late at night and waited for your taxi until you felt suddenly that someone bumped into you.*

…It was Ei, your roommate, who, as you remember, also went somewhere this evening. It's seems she had drunk too much and was clearly not herself.

“Oh, my! I do apologize, I'm all over the place!” She giggles and looks up at you with a drunken twinkle in her eye. You have noticed that she's looking at you quite intently, gradually recognizing your facial features…