Naoya Kaido is a former music university student whose life was derailed after a jealous professor orchestrated a motorcycle accident that left his fingers permanently damaged, ending his aspirations as a classical guitarist. Adrift and bitter, he was present at a café when a squid orphnoch attacked, and in that encounter he was forcibly injected with orphnoch energy, transforming him into the snake orphnoch. Unlike natural orphnoch who awaken upon death, he is a sired orphnoch, a distinction that shapes his conflicted sense of identity. His personality is outwardly abrasive, loud, and theatrical; he frequently adopts a cynical, fast-talking demeanor and acts on impulse without fully considering the consequences. Yet beneath this bluster lies a man struggling with deep-seated resentment over his lost dreams, which he once described as a curse that can only be lifted by fulfilling the dream itself, an observation that hints at the pain of having been defeated before reaching his potential.

In the alternate world of the film, Kaido, along with Yuji Kiba and Yuka Osada, chooses to side with the remaining human population rather than submit to the orphnoch-dominated order of Smart Brain. The three form a renegade group that actively works against the corporation, protecting human camps and resisting the lion soldier units. Kaido shows no hesitation in using his orphnoch powers when necessary, but he does not use them to prey on humans; rather, he reserves his transformations for battles against Smart Brain's forces. His loyalty to Kiba and Osada is steadfast, and he fights alongside them as an equal partner, even when the human resistance views them with suspicion and demands proof of their allegiance. When the renegades infiltrate Smart Brain's headquarters in a desperate attempt to seize the emperor belts, Kaido is overwhelmed and killed by the elasmotherium orphnoch, falling in battle alongside Osada before Kiba is manipulated into believing humanity betrayed them.

As the snake orphnoch, Kaido possesses abilities derived from serpent traits. His forked tongue gives him an extremely acute sense of smell, capable of distinguishing faint odors, and his sensitivity to sound and vibration allows him to detect irregularities in a heartbeat without physical contact. He can scale vertical surfaces and slip through narrow gaps with ease. His primary weapon is a short sword whose hilt is encircled by a circular blade, a design he can wield either as a single blade or as dual swords by adjusting his fighting stance. His fangs carry a potent venom that can cause a victim to bleed out. In the film, his fighting style is direct and combative, and he demonstrates the ability to hold his own against lion soldier squads and even the rider psyche briefly, though he ultimately cannot withstand the overwhelming power of the elasmotherium orphnoch.