Gosu, Hugungeuro Kkaeeonada

Once a notorious master of the deviant sects, Nyeon-Bi Cheon pays a hefty price for her romance with a man of a virtuous sect, Won Gae of the True-spirited Sword. As her lover poisons her to death with a dragonsbane fruit, Nyeon-Bi perishes with more questions than answers. When she wakes up, however, she finds herself in a different sort of peril, as she reincarnates in the body of Noble Lady So-Yeo Cheon, a concubine of the imperial palace. As So-Yeo, Nyeon-Bi must rely on her knowledge from her past life to navigate both intrigue and romance in the palace!

(Source: WEBTOONS, edited)