The Assassin Laughs at Twilight

A brilliant surgeon meets a tragic end during an earthquake while operating on his only sibling. Reborn into a mysterious otherworld as a deadly assassin, he must reconcile his past vocation with a new, morally fraught existence as a “revenger.” Just as he contemplates his shattered identity, a girl who mirrors his sister appears before him --–an uncanny echo that pulls him into a labyrinth of fate, duty, and supernatural suspense.

(Source: Titan Manga)