Shu enters his hideout for a quiet lunch only to find Inori, his #1 musical crush, bleeding on the floor. After he fails to stop her pursuers from hurting her more, his one shot at self-respect is to deliver a strange vial she stole to her terrorist pals.

GHQ is awash in blood, chaos and song. As the Cancer sweeps over Tokyo, Shu faces the truth about friendship and the consequences of inaction.