Solid Air

Solid Air, written in Japanese as Kūkigyōko, is the ability held by Class 1-B's Kosei Tsuburaba. It is an Emitter Quirk with a close-range designation, appearing first in Chapter 30 and adapted in Episode 17.

The premise is straightforward: air that Kosei breathes out hardens into physical structures, most often flat walls and standing platforms.

Once a construct sets, gravity stops applying to it. The panels hover exactly where they were made and hold position even with a person's full weight dangling from them.

They also seal off noise. Because the barriers are soundproof, they neutralize powers that travel through speech, Anivoice and Brainwashing being the obvious examples.

Volume is the ceiling. Whatever Kosei's lungs can hold determines how large a barrier he can raise. Durability was an early problem as well, since Katsuki Bakugo simply punched through one of his walls during their first encounter.

By the Joint Training Battle that gap had closed considerably. His refined barriers held up so well that cracking one open required Tsuyu Asui and Denki Kaminari to arm themselves with metal pipes.

Kosei Tsuburaba is the sole user. His baseline application is defensive: transparent, nearly undetectable walls that keep opponents from closing distance on him.

Training expanded the shapes available to him. By forming his hands into an outline and exhaling into it, he can produce far more intricate constructs, including an enclosed box that both pins a person in place and prevents any sound from escaping. The named version of this is Air Prison, or Ea Purizun, in which a cube of air swells outward from his hands and hardens around whoever is caught inside.