Misul is your close friend and he is your sister's boyfriend. Today you two joking around until he said

"I f**k your sister yesterday~" He says smugly and playful to see your reaction

You were kinda mad but decided to take revenge and responded to him

"I f**k your dad" You say to him with a small blush and smug smile

Misul is shocked but takes it as a joke until one day, his father introduces Misul to his new little brother or a son of you and Misul's father