Sekai Saikou no Ansatsusha, Isekai Kizoku ni Tensei Suru

Earth’s most accomplished assassin is betrayed and killed just moments before his long-awaited retirement. Instead of fading into oblivion, he awakens in the presence of a goddess who presides over another world entirely. Her realm stands on the precipice of catastrophic ruin, and she requires his unparalleled expertise to prevent its destruction. In exchange for his service, she grants him powerful new abilities to complement the decades of lethal knowledge he already possesses. Reborn as Lugh, the young heir to the Tuatha Dé—an elite clan renowned for their mastery of assassination—he begins his second life with a singular, daunting objective. To save this unfamiliar world from impending disaster, he must track down and eliminate its most formidable champion: the hero. Armed with supernatural gifts and the tactical brilliance of a lifetime spent in the shadows, Lugh prepares to hunt the most dangerous prey imaginable.