Item from Attack on Titan by Hajime Isayama
Spinal fluid injection that transforms Eldians into mindless Pure Titans. A weapon, a punishment, a last resort, and the cruelest gift anyone can give.
Titan serum is distilled from the spinal fluid of a Titan Shifter and, when injected into a Subject of Ymir, triggers an irreversible transformation into a Pure Titan — a mindless giant driven by the instinct to devour humans, specifically Titan Shifters, in the desperate biological hope of becoming human again. The transformation is immediate and violent. The person is gone. What remains is hunger and size. Marley uses serum to punish Eldian dissidents, injecting them on Paradis's shores and letting them wander as monsters. The Survey Corps kept a single vial as their most precious and terrible resource — a way to create a new Titan Shifter by having a Pure Titan consume an existing one. When Erwin lay dying and Armin lay burned beyond recognition, Levi had one syringe and two people he could save. The serum doesn't care about fairness. It never did.
Also known as: the serum, Titan injection, spinal fluid