Weapon (狂気, Kyōki) is the 50th chapter of the Kiseijuu manga series, written and illustrated by Hitoshi Iwaaki.
Uragami thinks about his past and what led him to be arrested. As Uragami continues to stare down Shinichi, he comes to the conclusion that he's not a parasite. After leaving, Shinichi talks with Migi about how Reiko may not have been bad, but that there are humans as bad as Uragami. Else where Hirama holds a meeting where they discuss a plan to elimate the parasites.