Kingdom Hearts Explained

Part 15

Riku kills his other self (but not the one he meant to), and Roxas is next
Sora takes the deal and goes under, but that's not the end of the shenanigans in Castle Oblivion! Remember Ansem the not-so-Wise from earlier? Well he's pissed and out for revenge (plus going by the name DiZ, for some reason), and decides to put his plan into action. Finding Riku in a nebulous darkness realm, he reveals that a piece of Heartless Ansem will always exist within the poor kid, but if he finds Namine, she can help him lock it away. So Riku heads on a journey of self-discovery (during which he finds and kills a Frankenstein version of himself created in a lab, which probably wasn't what he had in mind).

Along the way, he gains the nifty ability to change back and forth between Ansem and an older, blindfolded, emo version of himself. This comes in handy when he finds out about Sora's coma and Namine tells him the only way for Riku to wake the dipshit up is to take out some dude named Roxas. Okay, now we're getting somewhere!

Explained in: Kingdom Hearts: Chain of Memories, Kingdom Hearts 358/2 Days