Mustard

The mask registers first: a green shell that covers his face entirely, fed by hose from two oxygen cylinders strapped across his back. Under the gear he is slight and narrow, dressed in a black gakuran that marks him as a student, plus teal gloves and shoes in white. Unmasked, he shows tanned skin, brown eyes, and short light brown hair falling in loose waves.

The design borrows from the First World War throughout. His villain name is lifted from sulfur mustard, the gas notorious for its use in that conflict, and the mask and helmet lean on period equipment; the silhouette may also nod to Mamoru Oshii's Kerberos saga, which took its own cues from German wartime gear.

Patience is his creed. He would rather wait for the right moment than force one, and he judges support equipment purely by what it achieves rather than how it looks, a standard he throws in Himiko Toga's face. Whatever Quirk an opponent holds, in his view the person behind it is still only human.

Cruelty comes easily. He brought a firearm to the camp raid and tried to kill Tetsutetsu Tetsutetsu and Itsuka Kendo with it, and he kicked Tetsutetsu while the boy lay on the ground unable to breathe. Much of his venom aims at U.A. specifically: he mocks Kendo and Tetsutetsu as pitifully simple and too straightforward, insists their standing is handed to them by their school's name alone, and calls that arrangement proof of everything broken in society. He is also loud about his own skills and accomplishments, and boasting is a habit he rarely resists. Official material tags his personality with the phrase childish smooth talker.

Mustard fights with his head. He understands the limits of his own ability well enough to hold off two U.A. students at once, but strip away the gas and the gun and there is nothing left: no close-quarters training, no answer at arm's length. His marksmanship is genuine, precise enough to destroy Tetsutetsu's mask with one shot, and reading positions inside his own cloud makes the aiming easier.

That ability is Gas, which floods an area with a sleep-inducing haze on a huge scale. Movement inside the cloud creates fluctuations he can read, so nothing hides from him in it. The catch is that production has to be continuous, since the gas thins out fast the moment he stops, and he has no immunity to it himself, hence the mask and tanks he never removes. Alongside the breathing gear he carries a .38 revolver and ammunition.

Taken into custody after the training camp invasion, he gave the authorities nothing about the League. Alone among the Vanguard Action Squad, he never turns up in the story again.