Board Thread:General Discussion/@comment-3244769-20160228202309/@comment-31121580-20180424194141

any shinigami who has reach the requirement of reitsu can use bankai of course in renji case he forced it and thus receive half a bankai with Vice captain Reitsu. thus a True Bankai is awakened after a shinigami reaches Captain Level Reitsu.

rukia gained her bankai after reaching captain level Reitsu by eating Zero squad Food and training there, getting a bankai is easy since Ichibei can just tell rukia or renji its Name, and or use the same method urahara did which is prett much in hours