After losing in Chicken Invader 10, Lee jinki who is under the cover of Lee Raesun is so pissed with his dongsaeng for not playing hard in their mission so as a lesson he took the girl's precious drink and drank it without second thought. Rinrin's rage/silliness controlled her mind resulting her biting her unnie. (She doesn't know the truth, so she called Onew unnie not oppa)