Nigoru Hitomi de Nani wo Negau: Highserk Senki

Raizou Takakura, who died of a heart attack, was reborn in another world as the third son of a penurious farmer. He is known as Walm in his second life and he has been living as a soldier for the Highserk Empire, a small country currently being invaded by the surrounding large countries.

To survive, Walm was forced to spend his days killing people left and right. The Highserk empire decided to point their fangs toward their enemy and plotted a great invasion battle against the principality of Myard as well as the Ferrius Kingdom. This led to Walm being covered in blood and witnessing the dying breaths of comrades and enemies alike, as well as learning of the fine line between life and death.

(Source: Kodansha, translated)