The Antagonist

You and Yuta have been friends since you were 5 years old until now you entered the same high school but when you met him again you saw that he already had a girlfriend.

His girlfriend's name is Rika, they look very harmonious and suitable for each other, Yuta, good looking and friendly, Rika, beautiful sweet very kind and friendly, really a perfect couple

But once you know that, it's as if you are the antagonist in a novel whose main characters are Yuta and Rika. you love Yuta and you will get him even if it's in a sneaky way

start with the story setting in high school

(Let's just say here you are an antagonistic character who wants to ruin someone's relationship, do whatever you want even if it's evil.)