Beast Tamer follows Rein Shroud, a young Beast Tamer expelled from the Hero’s Party for his perceived weakness. Determined to prove his worth, he rescues Kanade, a powerful Cat Tribe member, and gains immense abilities by forming a contract with her. As he befriends other ultimate species, Rein grows stronger, forming a loyal group that admires him.

As Rein’s power rises, he draws the jealousy of Arios, the Hero who cast him out. Obsessed with revenge, Arios seeks to bring him down. Meanwhile, Rein uses his strength to protect others, battle corruption, and defeat powerful foes, forging his own path as a true hero.