The World's Finest Assassin Gets Reincarnated in Another World as an Aristocrat - Season 1 Episode 12
Battle of Assassin

Lugh and Dias father come up with a plan to fake Dias death and safely sneak her into to the Tuatha Dé region. Unfortunately, the arrival of Setanta MacNess thwarts the plan before they can enact it. As Setanta is the wielder of Gae Bolg, Lugh knows that he will not survive a direct confrontation with him, so he fires a magnetically propelled tungsten projectile into the atmosphere and stalls Setanta long enough for it to obliterate him. Afterwards, the Tuatha Dé family adopts Dia under the guise of being Lughs younger sister, completing the mission. Sometime later, Lugh receives word that the Hero, Lord Epona Rhiannon, has arrived in the Alvan Kingdom.