Zogundar said:
Ichigo being a Quincy goes all the way back to the very beginning, the very first chapter, guys. He absorbed Rukia's powers, remember? Not entirely unlike how the Vandenreich stole the Captains' Bankai.
And I really don't think Masaki was killed by Grand Fisher. He didn't remember her, he took that memory of her from Ichigo.
Rather than "Oh she suffered level decay" I'm thinking more likely that she was killed by someone very, very high on the food chain if she's stronger than Isshin.
And since she's the main protagonist's mother, may as well go all the way and assume it was whoever is at the top of the food chain (Or at least whoever will end up there as the last boss.)
Possibly that Shinigami who was shadowing Ichigo at the start of this arc.
Chapter 25 seems to hint at Ichigo's memory having been altered.
Its most likely shinigami who killed her when she was trying to deal with Grand Fisher after loosing her powers.