Crystallize allows Yu to grow a large number of crystals from his body, completely covering his skin with them.
The crystals are shown to be both durable and able to grow near-instantaneously. It does not appear to have any limitations to where crystals can sprout form his body. Yu also possesses the ability to form his crystals into a sword shape that covers his arm in order to extend his reach.
Despite their density, the crystals are not unbreakable. Yu also keeps his head shaved so that the crystals can grow smoothly, implying that hair may hinder the crystallization process. The crystals also tear through whatever clothes the user is wearing. According to Yu, the crystals generated with this Quirk do not possess any financial value, which was discovered when someone tried to salvage these crystals for profit, only to find out they were fake.