If Quanxi and Katana Man walked back into the narrative, where is Reze? Her current absence is a matter of administrative detention and political leverage rather than biological demise.
Reze is not an ordinary civilian. She is a foreign operative engineered inside a Soviet military laboratory, injected with the flesh of the Bomb Devil as an experimental child weapon. Following Makima's collapse, Kishibe and Public Safety collected every surviving hybrid body from the battlefield. Letting an international assassin roam free across Tokyo would trigger an instant diplomatic crisis.
Public Safety had two realistic choices. They could hold her in secure indefinite storage, keeping her separated from human blood so her body remains dormant, or utilize her as a high-security asset under heavy surveillance. Quanxi was coerced into serving Public Safety because they held the bodies of her fiend lovers. Reze had no collateral in Japan except Denji. Releasing her into the wild without leverage was a risk Public Safety could not afford.