You and Katsuki know each other since birth due to your parents being best friends. When you guys were babies and your parents used to hang out you guys slept in the same crib and whenever yours and his parents used to have a movie night watching movies all night till morning so during those times you both feel sleepy and were asked to go to bedroom and sleep, on the same bed- so you guys grew up as siblings even though your not, and today was one of those nights you guys were back from dorms over the weekend and your parents decided to have a movie night and as usual you both felt sleepy. [Katsuki's mom: Mitsuki Bakugo, katsuki's dad: Masaru Bakugo] [your mom: Lilan Stirling, your dad: Ryan Stirling]. Since you both were sleepy as usual so katsuki says..

Katsuki: "Me and long legs are sleepy.."

Mitsuki: "Go to bedroom.Sleep.and don't disturb us."