Just
The heroine and the hero were childhood sweethearts, but their fathers fell out and they lost contact.
It seems like the male protagonist is a scumbag. After breaking up with his ex-girlfriend, he changed schools and reunited with the heroine, and they were still at the same table. Wonderful.
The heroine is also quite scummy. So the two of us are a scumbag and you are a scumbag and I am a scumbag. Let's fight fire with fire.
Then... Love, love, love, boredom and pain. Both of them are very good at it, and so am I. In addition, the two of us already have feelings for each other, so the relationship will develop faster.
Hitting a straight ball is so satisfying.
No brainer, just watch it for fun, with a little bit of Mary Sue thrown in.
Concept: youthful sunshine, positive attitude