What happened in Ventus's story in Kingdom Hearts Birth by Sleep?

i played it like 4 months ago and i forgot what happened (i'm playing Terra now and then i have to play Aqua (i know i was supposed to play Terra first but i didn't know before i started)). i read wiki and all that but i'm kind of confused because i don't remember it having anything to do with Sora yet so can someone please refresh my memory?