@Grimm, why not have both factions be descendents of both the original members of nobunaga's squad and the jacks? That way the motives would remain the same, yet the characters would all be fresh. Doing it that way could also add an additional layer of emotional conflict across the collective cast. As most of the current denizens of the soul society would probably be oblivious to the events that transcended the ensuing chaos, forcing them to not only deal with the threat literally, but to also lust to uncover the history behind it as well.