ONIMAI: I'm Now Your Sister! Season 1 Episode 3

Mahiro makes a mad dash for the bathroom, but when he opens the door, he finds the facilities are already occupied by a high school girl he's never met. This bold fashionista turns out to be Kaede, Mihari's old classmate from middle school. Mahiro is initially a little nervous around her, but as he gets to know her, he learns how much of a nice person she is and becomes quite attached to her. Then, out of nowhere, Kaede asks "You've never done it before, have you?" and begins to scooch closer to a puzzled Mahiro. I wonder what she's about to do next...