Board Thread:Questions and Answers/@comment-8811717-20200710154155/@comment-10330822-20200727191717

Old Man Zangetsu, i.e. Quincy Zangetsu, primarily acts as the "guard" between Ichigo and his Shinigami Powers, so if he wasn't there then Ichigo would have had access to his full power from that start rather than simply whatever Zangetsu wished him to have. Although, if he didn't exist, it would be because Masaki wasn't a Quincy, which she was, and if she wasn't, then there would have been no need for Isshin to turn human to save her. Also, the essence of the White that was in Masaki wouldn't have gone to Ichigo because she wouldn't have stepped in against White and Isshin in that battle. Odds are in fact, if Old Man Zangetsu didn't exist than neither would Ichigo. Old Man Zangetsu is proof that Masaki was a Quincy, and even if Isshin married Masaki without her being a Quincy or infected by White, Ichigo would not be the same being, he'd simply be a human with Shinigami powers, and his Zanpakuto would not have been hollow-based.