Diamond Skin, Arifureta Vol 1

Diamond Skin involved coating the caster’s body in mana and then hardening it, so that they were surrounded by a shell literally as hard as diamonds.
He hadn’t trained it much yet, so it was probably barely even a tenth as strong as the cyclops’ version of it had been.
Still, it was enough to stop Yue’s wind blades, which were sharp but lacked power.