Mamonogurai no Boukensha: Ore dake Mamono wo Kuratte Tsuyoku Naru

Rudd is an E-rank adventurer whose only skill, status immunity, has left him mocked and relegated to gathering herbs in poisonous labyrinths. When a party finally hires him as a porter, he thinks his life may be improving, only for his companions to use him as bait for a dungeon monster and abandon him to die.

Wounded and out of supplies, Rudd breaks a deadly taboo and eats monster flesh to survive. He discovers that doing so allows him to inherit abilities from what he devours. The niche skill that made him an outcast becomes the foundation of a power nobody else possesses, beginning his rise from despised forager to an adventurer who grows stronger with every monster he dares to consume.