Kosei Tsuburaba, a Class 1-B student at U.A. High School, trains diligently to become a pro hero. His spiky brown hair and large oval eyes with black pupils frame a face marked by determination. His hero costume features a light blue high-collared jacket over a black undershirt, pale pants with gray kneepads, and sturdy brown boots with cylindrical soles. Standing 170 cm tall with blood type O, his May 19 birthday and Kagawa Prefecture roots trace back to Hadoma Middle School. Blending enthusiasm with pragmatism, Kosei balances high personal standards with occasional competitive taunts, as seen when provoking Katsuki Bakugo during the U.A. Sports Festival. Known as one of Class 1-B’s “common-sense kings” alongside Sen Kaibara, Yosetsu Awase, and Hiryu Rin, he exhibits a calmer demeanor than peers while thriving as a tactical support player. A sly, playful side emerges in moments like his flustered reaction to Tsuyu Asui’s tongue capture during training. His Quirk, Solid Air, lets him solidify exhaled breath into invisible barriers or platforms. Early limitations saw these constructs shatter easily, but rigorous training boosted their durability to withstand repeated metal strikes. Lung capacity dictates their scale, requiring strategic deployment. A refined technique, Air Prison, traps foes in soundproof boxes—effectively countering voice-based Quirks like Anivoice or Brainwashing, as demonstrated against Koji Koda and Hitoshi Shinso in the Joint Training Arc. Kosei’s growth shines through key battles: ranking 23rd in the Sports Festival obstacle race, joining Neito Monoma’s cavalry team, aiding defense during the Forest Training Camp attacks, and collaborating with Jurota Shishida to ensnare opponents in the Joint Training Battle. Though ultimately captured by Asui, his tactical use of Air Prison to temporarily immobilize Shinso underscored his refined skills. The Ultra Analysis Book rates his abilities at 2/6 power, 3/6 speed, 5/6 technique, 4/6 wits, and 5/6 backup, emphasizing technical support over brute strength. He admires Shoto Todoroki and bonds with Class 1-B’s pragmatic circle. Outside heroics, he enjoys ball sports and retro special-effects shows. While his hero name remains undecided—possibly derived from his real name—his strategic contributions and evolving Quirk mastery cement his role within Class 1-B’s dynamic.