i think soul society, if im remembering the arc names right, works well coming off of the first one. where the first arc builds the relationship between ichigo and rukia, as well as with ichigo's friends, arc two is like the protagonist going into hell to save someone they love. things just keep getting worse and worse, but the protagonist persists (with shonen flair). it does get generic as it breaks down into fight after progressionless fight and "hnng would you like to see my bankai." and it ultimately ends super badly in terms of character arcs and emotional momentum (the aizen twist was still cool!). the wasted relationship between rukia and ichigo is just one part of it (even if they were just to remain friends, they should have gone forward as co-protagonists!). it just never rebuilds that emotional connection, buries itself in the same shit that destroys all of the worst shonen jumps.