Finished 358/2 for the first time on ps4 [KH358]

Just some questions. It was fantastic. So many unanswered questions finally came to light and I'm super excited to hop into KH2 right after this. But I'm wondering as to what did Riku do at the end with Roxas was he the one that reset his mind? So that's who we have at the beginning of KH2? Also does he power up into Ansem? Using dark energy.