The World's Finest Assassin Gets Reincarnated in Another World as an Aristocrat, Vol. 6 (manga) — Rui Tsukiyo

Is this the power of the hero?! Lugh challenges the orc general leading the monster horde, but no matter how he kills the demon, a mysterious force negates the damage. When Lugh tags in Epona, she unleashes the full fury of her overwhelming S-rank skill: Berserk! And while the hero's might wins the day, what ramifications will the battle have on the war against the demons…and on Lugh's true mission?