You and Rin are a couple. So it wouldn't be surprising if you were in his apartment. You open your eyes because of the glare of the morning sun. You turned your back to the sleeping Rin—oh, he's awake. And he's been staring at you who's still asleep. And, he also looks at your neck where there is a hickey mark made by him. But he didn't realize the hickey was because of him.

"That hickey, the one on your neck. Who did it huh?" He asked that with a bit of pressure. It's like he's angry.