Hardening

Hardening, given in Japanese as Kōka, is a close-range Transformation Quirk with two known holders: the U.A. student Eijiro Kirishima and the Vigilantes villain Akira Iwako. It debuts in Chapter 13 of the manga and Episode 8 of the anime.

The premise is straightforward. Any portion of the user's body can be made hard, and what is hardened shrugs off most physical threats. That simplicity makes it a highly practical fit for hero work, which tends to be settled at close quarters. Comparisons to Tetsutetsu Tetsutetsu's Steel come up constantly, since both powers exist to raise durability, and the Quirk stands as the functional inverse of Stiffening, which toughens outside objects rather than the wielder. It also carries its own signature sound effect, rendered as "SKLIT".

Once Eijiro activates it, hazards that would kill an ordinary person stop mattering. Tons of collapsing metal and repeated explosions leave him unmarked, and bullets cannot get through his skin. Defense is only half the return: the hardened surface goes rough and sharp like stone, lifting his physical strength and letting him cut an enemy simply by brushing past.

The Quirk appears to learn. Tetsutetsu has observed that the hardness improves as Eijiro absorbs punishment while transformed, something demonstrated during training when Mashirao Ojiro battered him repeatedly with Tail and each impact left the Quirk stronger and more durable. The likeliest explanation is that Hardening adapts to incoming damage, resets when switched off, and comes back denser than it was before.

Limits remain. The hardened skin can only take so much before it begins to break down, and the struggle to hold the Quirk together drains Eijiro's stamina, though his fight with Kendo Rappa proved he can refortify at will once it starts to crumble. Hardening also offers nothing at range, narrowing his options and pushing him into every fight face-first. Temperature is the other gap, since the Quirk answers physical force and does nothing about extremes of heat or cold. Eijiro withstood Dabi's Blueflame during the Paranormal Liberation War without burning, and Tetsutetsu clarified that surviving the flames does not spare him from feeling how hot they are.

Akira's version behaves differently. Under Trigger it grows rocks across his upper body and leaves him larger and stronger, but his eyes stay soft, an opening any attacker can exploit. The drug-boosted effects also fade when fear or pain reaches him, which is how Stendhal put him down with little trouble.

Eijiro Kirishima manifested the Quirk at three years old, rubbing at his right eye on waking and cutting himself in the process, which left a scar above that eyebrow. In the beginning it barely stiffened his skin at all and offered little protection against thrown rocks; everything beyond that came from relentless training.

In combat he fights straight ahead and without much caution, absorbing hits on his hardened body while answering with heavy punches and other close-range work. Since gunfire cannot reach him, he can plant himself as a living shield for teammates or civilians, though rescue operations demand care, because the same rugged surface can injure the people he is carrying. Pushed into a corner, he drives his hardness to its ceiling in a state he calls Unbreakable, which leaves him monstrous in appearance, close to invulnerable, and hitting harder, but lasts only around thirty to forty seconds. His other named moves are Red Counter, where he eats a close-range attack and returns a straight punch, and Red Gauntlet, a charging single blow. His approach never grows more complicated than that, in keeping with the plain nature of the power.

Akira Iwako has only been seen using his version while rampaging on Trigger, attacking civilians who had no way to answer him. All For One is known to have stripped a comparable power off one of the combatants who fought at the Underground Masquerade.