Magical constructs.
They were basically humanoid machines created with a mix of technology and mana, though as the development of the former in Taia hadn't gone far, their power couldn't surpass the D rank without sacrificing a monstrous amount of mana, which was simply not cost efficient.
The reason for Ezekiel's curse was the very nature of the constructs. With their appearance, both Vahn and Yuri would have their advantages in battle–which they gained due to the unique nature of their magic–gone. After all, both Life and Death magic couldn't work on inanimate objects, there were no parts to heal or debuff so to speak.
Yuri could still help a bit, she had tinkered and modified some of the few death spells she knew, gaining the ability to create solid attacks that could work. Vahn, on the other hand, would have to rely on his battle techniques and internal Life magic spells. He would be unable to deal any damage to the constructs alone.
