Arata is the shared name of the two central protagonists in this narrative, a boy from a fantasy realm and a boy from modern Japan, whose fates become intertwined when they magically exchange places. The Arata from the world of Amawakuni is a fifteen-year-old member of the Hime clan, a matriarchal family responsible for providing the princess who maintains balance in the world. Because no girls have been born into the clan, he has been forced by his grandmother to disguise himself as a girl to take on the role of the princess's successor. During the succession ceremony, he witnesses the assassination of the current princess, Kikuri-hime, and is subsequently framed for the murder by the Twelve Shinshou, the princess's personal guards, forcing him to flee for his life. In his escape, he enters a mystical forest and is swapped with his counterpart.

This Arata is characterized as an outgoing, energetic young man who is easily bored. He is brash, boyish, and goodhearted, possessing a strong sense of justice and the physical strength typical of a shonen hero. In contrast, Arata Hinohara is a shy, quiet, and deeply insecure high school freshman who lacks self-confidence. He is haunted by intense bullying from his middle school years, which has left him determined not to stand out or attract attention in his new school, despite his natural athletic abilities. When the bully from his past, Kadowaki, transfers to his high school and begins tormenting him again, causing his new friends to abandon him, Hinohara becomes bitter and cynical, ultimately wishing he could disappear from the world. It is at this moment of despair that he is pulled into the other Arata's world.

The core motivation for the fantasy-world Arata is survival, as he is wrongly accused of murder and hunted by the powerful Twelve Shinshou. For Hinohara, his initial motivation is simply to find a way to return to his own world. However, upon arriving in Amawakuni and being mistaken for the other Arata, he is entrusted with a sacred Hayagami, a sword-god named Tsukuyo, and accepts the dying wish of the true princess to restore order. This quest places him directly in conflict with the Twelve Shinshou, who each possess their own powerful Hayagami. His role in the story evolves from a frightened, reluctant participant to a determined hero who fights to protect others and fulfill his duty. The fantasy-world Arata, meanwhile, finds himself in modern Japan, taking on the identity of the high school student, and his role is to navigate this unfamiliar world and the challenges of Hinohara's life.

Key relationships drive the development of both characters. For Hinohara, his relationship with Kotoha, a childhood friend of the other Arata, is crucial, as she becomes his loyal companion and healer in the fantasy world, and her belief in him helps him grow. His antagonistic relationship with Kadowaki, the bully who also eventually crosses into Amawakuni, forces him to confront his past traumas and insecurities. The other Arata forms a significant bond with a girl named Oribe in the modern world, feeling that this meeting is the very reason he was brought there. Both Aratas also share a unique connection to each other, as their swapped existences force each to see themselves and their worlds from a new perspective.

The development of Arata Hinohara is a central focus of the story. His time in the dangerous world of Amawakuni forces him to find his inner strength and put his trust in others. Initially a boy who feels his life has no meaning, he grows to understand that his purpose is to protect those who cannot protect themselves. He learns to love himself and vows that his life does have value. This is a significant journey from the deflated, lonely boy who wished to disappear. The fantasy-world Arata also undergoes change, adapting to the complexities and social dynamics of modern high school life.

Both versions of Arata possess notable abilities. Hinohara, in his original world, was a talented track athlete with impressive speed, though he initially hides this ability. In Amawakuni, his primary power comes from his role as the wielder of the Hayagami Tsukuyo, also known as the Sovereign of the Sun, a primordial sword-god of light and the origin of all other Hayagami. Through Tsukuyo, he can perform powerful techniques such as Kisara, Raisenha, and the ultimate attack, Sosei no Hinowa, which has the ability to purify other Hayagami that have been corrupted. The fantasy-world Arata, while not a wielder of a Hayagami in the same way, is a capable and athletic individual who uses his wits and physical prowess to survive in the unfamiliar modern setting.