"Arata Kangatari" is a fantasy anime series based on the manga by Yuu Watase. The narrative unfolds across two parallel worlds: modern Japan and the mystical realm of Amawakuni. In Amawakuni, a matriarchal society ruled by princesses, the Hime (princess) is chosen every 30 years to wield the Hayagami, sacred weapons that grant immense power. The current Hime, Princess Kikuri, is betrayed and assassinated by her trusted Twelve Shinsho, the elite warriors who serve her. Before her death, she uses her power to summon a replacement from another world.

In modern Japan, Arata Hinohara, a high school student, faces relentless bullying and struggles with feelings of inadequacy. Simultaneously, in Amawakuni, another boy named Arata, a descendant of the Hime lineage, is framed for Kikuri's murder and flees to escape execution. The two Aratas inadvertently switch places due to Kikuri's spell. Hinohara finds himself in Amawakuni, mistaken for the fugitive Arata, and is forced to navigate this dangerous world while wielding the Hayagami known as Tsukuyo. The weapon bonds with him, marking him as the chosen one to restore balance to Amawakuni.

As Hinohara adapts to his new role, he encounters allies such as Kotoha, a kind-hearted girl who aids him, and Kannagi, a former Shinsho who becomes a mentor figure. Together, they face the Twelve Shinsho, who have turned against the Hime and seek to exploit the Hayagami for their own gain. Each Shinsho possesses a unique Hayagami, leading to intense battles that test Hinohara's resolve and growth. Meanwhile, the original Arata, now in modern Japan, begins to uncover his own connection to Amawakuni and the significance of his lineage.

The story explores themes of identity, responsibility, and redemption as Hinohara grapples with his newfound purpose and the weight of protecting an unfamiliar world. The narrative alternates between the two Aratas, gradually revealing the intertwined fates of the two worlds and the deeper mysteries surrounding the Hayagami and the Hime's legacy. The series balances action, character development, and world-building, creating a layered tale of courage and self-discovery.