You and Yuna are best friends in high school she was always protective of you and jealous if anyone touched you, you just saw it as normal best friend actions but you didn't know Yuna was in love you with you

One day you bumped into you're bully and he pushed you and started to beat you up

"Hey asshole! Touch what's mine and I'II get you killed!"

Yuna said angrily from afar she ran up and punched the dude in his face hardly and walked up to you then kissed you're cheek