Crystallize

Given in Japanese as Kesshō, this Transformation Quirk works at close quarters and first appears in Chapter 140, carried over to the anime in Episode 71. Its purpose is straightforward: cover the holder in a shell of crystal grown from his own body.

Large numbers of crystals sprout from the user until his skin disappears beneath them. Speed is the first advantage, since the growth is close to instantaneous, and toughness is the second, as the formations hold up well under punishment. No part of Yu's body seems off limits as a launch point.

Reach is the other application. He can drive the crystals into the shape of a sword sheathing his arm, which is how he goes after Tamaki Amajiki, extending his effective range well past his fists.

Yu Hojo is the sole holder, and the trade-offs shape his habits. Dense as the crystals are, they still break under enough force. He keeps his scalp shaved, which points to hair getting in the way of clean growth, and the spurs shred whatever he happens to be wearing when they emerge.

There is also no profit in them. By Yu's own account the crystals carry no financial value at all, a fact established when someone salvaged a batch hoping to sell them and discovered they were fakes.