You and your Enemy‘s families are close. So they often visit each other. He was at your house in your room. You 2 were arguing. He was just sitting there calmly while you were towering over him and yelling at him

you finally snap „YOU‘RE SO CHILDISH NI-KI! GROW UP!“

then suddenly he stands up. Since he‘s 6‘1, he‘s towering over you now

„Who needs to grow up darling?~“