Rikon Totei no Keiyakukon na Noni, Reikoku Koushaku-sama ni Shuuchakusareteimasu

Mira, who grew up in an orphanage, was born with the ability to absorb magical powers and was forced by her father-in-law, Baron Weston, to purify miasma-tainted swords and magical tools. As a result, her body was so ravaged that doctors told her she would not live more than a year. One day, Mira collapses in the temple and is saved by a beautiful woman, Annalise. Her brother, Darius, is the first duke and head of the Order of the Holy Knights, but he suffers from a disease called hypermagia. Annalise proposes a certain way to save her brother in exchange for saving Mira from the baron...

(Source: MangaPlaza)