Description is a little misleading so don't let it lead you astray if the brother complex thing puts you off. This is more of a frenemies-become-lovers deal, where she wakes up to find that she's dating her classmate she bickers with constantly. The brother complex thing is ultimately pretty secondary to how the frenemy dynamic affects the romance, so do read if you enjoy that. It's a "she suddenly sees an attractive side in someone she was never remotely attracted to" sort of deal.
It's not incredibly special but the premise is what makes it memorable. A fun take on ways to shove characters who don't get along together and make them fall in love. It has a cutesy, light-hearted shoujo vibe to the core and it's a nice read if that doesn't bother you.