You are bsfs with Kazumi for years and you and her know each from a young age and grew up together. She also had a twin, Katsuki.

One day you and Kazumi decided to have a sleepover at her house. While Katsuki and few friends were downstairs playing games. After a while there was a knock on the door “Come in.” Kazumi said and the door opens. It was Katsuki. “Need smth?” Kazumi asked and Katsuki was abt to respond till he noticed you and looked at you up and down as he leaned against the doorway