Oxy-Man

Ash blond hair sits on a young man of unremarkable height and build. Nothing about his frame suggests a fighter.

His villain kit runs almost entirely to black: a jumpsuit, gloves to match, and a wireless headset. Transparent blue goggles let him keep his eyes open underwater, and he carries a spear as his weapon.

His unnamed Quirk produces oxygen inside his own body, so being submerged carries no risk of drowning for him. That single trait is what put him in the water at the U.S.J. rather than anywhere else in the building.

Beyond the Quirk he brings nothing but the spear. He is classified as an Emitter.

Once the League breached the facility, he and the other villains whose Quirks suited water made straight for the flood zone and waited. Kurogiri's Warp Gate eventually dropped Tsuyu Asui, Izuku Midoriya, and Minoru Mineta into exactly that spot. The villains had the numbers by a wide margin but hesitated, unwilling to commit without knowing what the three students could do, before finally moving in.

The fight lasted moments. Izuku drove a Delaware Smash into the water's surface and spun up a whirlpool that pulled the villains in, Minoru scattered a mass of sticky spheres across the water and glued the whole group to each other, and Tsuyu carried her two classmates out on her Frog Quirk. Stuck fast and unable to act, Oxy-Man and the rest were still there once U.A.'s staff turned up with the police, and he was arrested along with everyone else.