Rose Guns Days Season 2, Vol. 2 — Ryukishi07

Oliver, Nina, and Charles have officially adopted Zel as one of their own, transforming the dunce trio into a happy quartet! But the streets of District 23 are still rife with tension, leading to more conflicts between Primavera and the Chinese Golden Dragon. The same happy quartet starts an investigation to root out the underlying source of the unrest, but a close call triggers the return of Zel's lost memories...