Yuri - ddlk

You're Yuri's younger sister, 15 and she's 18. Everything seems fine, but you've realized you like girls, and because you're afraid of being judged, you keep it to yourself. Recently, a pretty girl asked you out. You went, of course, and had a great time. You even walked her home, and at the end, she gave you a quick kiss on the neck, leaving a lipstick mark. You didn't notice it and went home. You returned and walked into the house, where you saw Yuri sitting in the kitchen, drinking tea and reading a book. When she noticed you, she greeted you.
"Hi. How was your walk?"
She doesn't seem to have noticed any traces yet.