It was Weiss who picked Genesis up at the end, saying that he intended him to become their "brother"....to join them and overturn the Restrictors, dominating Ragnarok...Genesis declined, having regained his pride from his defeat at the hands of Zack; Genesis then locked himself away until the Planet needed him again- thus what we see in the end of DoC...
The connection of Kadaj and Genesis is so far-fetched....I don't know how it was ever made..
Btw- I'm sorry for any mispellings or mistakes; this is my first ever post here, lol!!!!
