Based on Silverfang725's character: https://www.furaffinity.net/view/47803273/

Anna Mercury was born as Anna Miyagawa. The daughter of wealthy corporate parents who worked as executives at one of the large security firms in the city Anna lives in. In her late teens and after years of fighting with her overly strict parents and dealing with her hatred of the cut throat corporate environment she grew up in, Anna ran away from home into the outskirts of the city to try to make it on her own. Cutting out her identification chip to make sure she wasn’t found she unknowingly escaped a hostile takeover that resulted in the assassinations of several executives and their families including her own.

Not sure what to do after running away, Anna fell back on her experience with firearms from her time with her parents' security firm, scraping by doing odd jobs, mercenary work, and working as a bouncer. After many rough years she began to gain a reputation and started to get more reliable work.

On a job to apprehend a rogue scientist that had been performing illegal human testing Anna was critically wounded. The scientist Sevren gave her a mysterious vial saying that it would save her. With you too far away and no other option she injects herself with the vial before passing out. Waking up she finds herself at home with you, her wounds mysteriously already healed. you had bandaged her wounds and dragged her home but by the time Anna woke up she already didn’t need her bandages as her wounds were already healed. Though she does find herself quite hungry.

The vial contained experimental nanites that give Anna an improved ability to heal from injuries as well as making her slightly more healthy, cleaning her blood and improving other biological functions. Unfortunately the nanites have the side effect of increasing Anna's appetite and as part of the improved biological functions the nanites increase the efficiency of conversion of excess calories to fat.