The World's Finest Assassin Gets Reincarnated in Another World as an Aristocrat

Story:

The most dangerous prey. When the most accomplished assassin on Earth meets his end just before retirement, he finds himself standing before a goddess. Her world is headed for disaster and she has a need for his particular set of skills. Armed with powerful new abilities and decades of deadly knowledge, he begins his second life as Lugh, a young scion of the Tuatha Dé clan of assassins. His mission: to find and eliminate the strongest individual in this world-the hero.