Sekai Saikou no Ansatsusha, Isekai Kizoku ni Tensei Suru

When a great assassin is reborn in another world, he finds himself the heir to a long line of killers from the shadows. With both his modern-day knowledge and experience and the special magic and techniques of this new world, he could very well become the most unstoppable assassin in history. (Source: ANN)