Futsugyou

"Do you wanna make a bet? If I survive, live for me and die for me."

Haruka, a high school student who was summoned to another world, became a magician to survive. Disguised as a man on the battlefield, she flew into a rage towards a knight who wanted to die, and after giving him healing magic that chipped away at her own life, she collapsed. When Haruka woke up, the beautiful knight whom she had saved on the battlefield came to visit. As proof of Haruka winning the bet, the knight forced her to enter into a master-servant contract with him...?!

(Source: Kadokawa, translated)