The Useless Snake Became My ProtectorEpisode 1

At graduation, I was publicly abandoned by the White Tiger Beastman, my companion of eighteen years. Everyone mocked my D-rank ability, except for the Black Serpent Beastman, who was called a "useless experimental subject," who was willing to bond with me. But when the poisonous tide descended, he devoured countless deadly poisons, transforming into a colossal serpent that blotted out the sky; and I finally discovered—my ability was not D-rank at all.