Revenge with the Demon King

She, an infamous fool in the capital, a loser in everyone's eyes, is set up by her vicious elder sister and perishes. When she wakes up, a modern girl's soul is reincarnated in her body. From then, she is no longer the pushover but becomes "the avenger". Her vile-hearted sister and heartless fiancé… must kneel before her and beg for their lives!

(Source: Webcomics)