I'm looking for an anime that involved a side-story where a certain young girl (she was probably a grade-schooler and the guy was a high-schooler) liked the male main protagonist of the story. I remember that the girl confessed to the main protagonist and was dumped because (of course) of being too young and the male protagonist liked the female protagonist. I'm not sure if the girl was relatively younger than the main protagonist, but she probably was (based on my vague memory). There was a boy who was younger than the girl who had a crush on her (not really sure) and she was a bit cold to that boy, saying that she might end up just like what happened to her.
In the end, when they grew up, the girl and the younger boy ended up together. I quite remember the scene where the younger boy was waiting on the couch and was saying something like "oneesan, hurry up". And then it revealed that it was the girl the boy (who was then a teenager) was referring to and that they were a couple.
I'm sorry for being vague but I really can't remember. As far as I can remember, the graphics are like in Special A and I guess the story was too (those kind of stories where there is a club and everything revolves around the club members liking each other etc.).