it's not out of nowhere. in ep1 where rei just collapses in front on rintaro is not a coincidence.
it will be revealed later that she intentionally got out of the car and collapsed in front of him to get his attention.
because she knows rintaro from childhood.
I don't mind the trope of "they met when they were kids" but it almost never actually adds anything to the story, so it feels like wasted content. Homie's not just gonna change his mind on dating an idol because they met one time as kids. This is a romance manga, he's in denial for another 50 chapters probably. 💀