Solid Air allows Kosei to solidify air to form a wall or platform through his breath.
Air walls do not fall to the ground once solidified and will stay afloat in midair even when another person hangs onto it. They're soundproof as well, making it effective against Quirks that rely on sound like Anivoice or Brainwashing.
The size of the air barrier depends on Kosei's lung capacity. The barriers are breakable, with Katsuki Bakugo being able to punch through one of them. By the time of the Joint Training Arc, Tsuburaba has improved his Quirk, making his barriers much more resilient, with Tsuyu and Denki needing metal pipes to bust them. It's unknown whether or not he can make more specific objects with his quirk, like weapons, or when he could even learn to do so.
Kosei uses Solid Air to create nigh-invisible transparent barriers for defense, preventing opponents from getting close.
After strengthening his Quirk, Kosei became able to create more elaborate and durable air constructs, like an air cube that can restrain people inside it while cutting off their voice from leaving to the outside world. He does this by shaping his hands around his blown air.
- Air Prison (エアプリズン Ea Purizun?): Kosei uses his hands to form a cube shape. Once he blows, a cube of air expands and solidifies into a soundproof box that traps whoever is caught inside of it.
- ↑ 1.0 1.1 My Hero Academia Manga and Anime: Chapter 30 (p. 2 - 3) and Episode 17.
- ↑ My Hero Academia Manga: Chapter 196.
- ↑ My Hero Academia Manga: Chapter 195 (p. 14).