Tomosato Ogino, who was an excellent doctor, was killed in an earthquake while operating on his younger sister. However, before he knew it, he had been reincarnated in another world, and had been given the vocation of an ``assassin,'' specializing in the ability to kill people. While he is struggling with his separation from his sister and his own calling, a girl who looks exactly like his sister appears in front of him. A fantasy suspense story about a parallel world.