Restricted to an abandoned mansion on the outskirts of London in fulfillment of a promise to her father, lonely Cardia lives day to day isolated from the world. Her body carries a deadly poison that rots or melts anything her skin touches, prompting the locals to call her a “monster.”
One day, her quiet solitude is interrupted as the Royal Guards break in to capture her. It is then that Cardia meets Arsène Lupin, a chivalrous thief, who helps her escape the soldiers' clutches. She soon finds herself on a journey with Lupin to locate her father, who holds the answers to her mysterious condition.
Summary taken from: MyAnimeList