Kyō Sematei is the older brother of Ryou Sematei and a supporting figure who becomes an antagonist in the battle royale known as KamiErabi. In the original reality, Kyō died from a severe illness, leaving his younger sister Ryou deeply affected by the loss. However, Ryou possesses the ability to create parallel worlds based on her imagination, and within one such world Kyō continues to exist, effectively revived. He appears as a participant in the god selection contest and opposes the protagonist Goro Ono and his allies.

Kyō is defined by a fierce protective instinct toward his sister. He resents the unfairness and suffering of the real world, which he believes caused their family's tragedy. His primary motivation is to use the power of the KamiErabi to create a new reality where Ryou can live happily and without pain. This desire leads him to approach Goro with a proposal to reshape the world together, but when Goro refuses, Kyō becomes a direct enemy. He is willing to fight ruthlessly to achieve his goal, viewing other candidates as obstacles.

His relationship with Ryou is the emotional core of his character. He acts as her caretaker and sole support, and his actions are driven entirely by his wish to protect her. His interactions with Goro shift from negotiation to confrontation as the story progresses. Kyō’s development involves a gradual reckoning with the true nature of the parallel world and his sister's own wishes, which may not align with his plan.

Kyō’s notable ability is called the Agan, which allows him to freely access and materialize elements from the parallel worlds that Ryou creates. He can summon weapons, barriers, or even alternate versions of himself, making him a formidable fighter. This ability is tied to his sister’s power, emphasizing their interdependence. Kyō is physically marked by an eye patch over his right eye, and his eyes are heterochromatic—red on the right and green on the left.