The Spirit Rejected Me, so I Gave the Contract to My Sister

Mystia, a young lady aspiring to become a spirit user, puts in a lot of effort and succeeds in summoning three spirits and forming master-servant contracts with them. However, her stepsister's machinations lead to the spirits terminating the contracts. With her stepsister taking away the three spirits, Mystia sinks into despair. Then, suddenly, a fourth spirit appears before her, one she herself had summoned without even realizing it...!? "My name is Skia. Those traitorous spirits don't understand the talents you possess."

A master-servant contract fantasy featuring a hardworking, unlucky young lady and a possessive great spirit!

(Source: Kadokawa, translated)