Eijiro's Quirk gives him the power to harden and sharpen any or all parts of his body, causing his flesh to become jagged and rock-like.There is a limit to how much damage his hardened body can withstand, which causes the Hardening itself to slowly dissipate, and Eijiro to lose stamina from struggling to keep his Quirk active. However, he learned that he can completely refortify his body.