Mushoku Tensei: Gilgamesh, the Third Prince

Gilgamesh, the strongest king of Uruk, unexpectedly reincarnates in another world as a prince of the Asura Kingdom. Most of his memories from his previous life have faded. The only things he remembers are his name and his absolute pride as a king. The original owner of this body had made countless enemies and was just secretly poisoned and assassinated. Every assassin in the room lies dead, and he alone has been reborn in the body. He wakes to corpses all around him and blood covering the floor. The commoners who plotted against a prince and schemed for power are nothing but insignificant ants in his eyes. Barefoot and bloodstained, he takes up his sword and walks out.