Futsugyou: Dansou Majutsushi to Kin no Kishi
払暁 男装魔術師と金の騎士
A woman named Halka, who disguises herself as a man and practices magic, uses healing magic on a battlefield to save a dying knight. After using the magic, which costs her part of her life, she wakes to find the knight offering her a contract. He claims it is a reward for winning a bet, and insists she agree to a master-servant bond with him.