this is a scene from clannad yes, its importance is the girl in the middle found out she is the ghost of a girl from a hostpital and now everyone is forgetting her and then being unable to see her making her disapear completely

so the thre of them stayed overnight at the school in an attempt to force themselves to not forget the next day the two kids on the outside were talking to a counciler at there school when they suddenly realize they had forgotten her and when they remembered she suddenly appeared again.