I need help finding an anime, all I remember is a guy is trying to get into a school but a girl gets him sick and it turns out the girl is his sister or something but the guy doesn't know this.

the anime isn't NAKAIMO - My Little Sister Is Among Them!, the style is older.

It isn't Koi Kaze as both siblings were both almost adults or late teenagers.

I found it, It was called Sakura diaries and the girl was the dude's cousin. I seen before but i forgot about it.