Ukyo Saionji, referred to in the series simply as Ukyo, is a supporting character in Dr. Stone: Science Future. Before the petrification of humanity, he served in the Japan Maritime Self-Defense Force as a submariner and sonar operator, a background that shapes much of his role in the stone world. His most defining trait is his extraordinarily sensitive hearing, developed during his sonar training, which allows him to detect faint sounds and pinpoint the exact location of a person or object by sound alone, even across great distances or in total darkness.

In appearance, Ukyo is a slim yet toned young man of average height with short white hair, green eyes, and round boyish facial features. He typically wears a relaxed, laid-back expression and dresses in a long, baggy orange top with a loose turtleneck, almost always accompanied by a matching paper cap.

Personality-wise, Ukyo is calm, reserved, and deeply principled. He is thoughtful and analytical rather than impulsive, and he consistently advocates for non-violent solutions to conflict. He believes that life should be preserved wherever possible and pushes for strategies that avoid killing, even when dealing with enemies. He is not inflexible, however; when peaceful options are truly impossible, he relents and accepts the need for force, though he strives to keep casualties to zero. His strong moral compass and steady judgment make him a voice of reason among his allies.

Ukyo is introduced as a member of Tsukasa Shishio's empire, where he serves as a skilled lookout and one of the strongest fighters in the faction. During this time he handles intelligence gathering for Tsukasa's side. His path changes when he communicates with Senku Ishigami and Gen Asagiri through a buried telephone. Impressed by their ideas and convinced that the Kingdom of Science offers a better future, he defects and joins them, but only on the condition that their methods will not involve killing anyone. Within the Kingdom of Science, he becomes one of the Five Wise Commanders and is placed in charge of security and intelligence gathering, duties that make full use of his sharp senses and vigilance.

His key relationships reflect his loyalty and integrity. He is initially loyal to Tsukasa but ultimately turns away because he cannot accept the empire's ruthless disregard for life. With Senku he shares a bond built on mutual respect and a shared vision of rebuilding the world, and he works closely with Gen, whose preference for psychological trickery aligns with Ukyo's desire to resolve conflicts without bloodshed. He also develops a close working partnership with Ryusui Nanami during the voyages of the ship Perseus, the two cooperating during the expedition to America that forms the setting of the Science Future storyline.

Throughout the story, Ukyo develops from a soldier of a rival faction into a trusted senior member of the Kingdom of Science. After the major conflicts of the stone world are resolved and the groundwork for rebuilding civilization is laid, his intelligence, diplomatic manner, and consistent moral integrity lead to him being chosen as a senior official in the reconstruction government, a role that suits his thoughtful and principled nature.

In terms of abilities, Ukyo's exceptional hearing makes him an invaluable scout and sentry, able to track movement, detect hidden threats, and relay crucial information during operations. He is also a highly skilled archer, capable of hitting targets with impressive accuracy. Additionally, he is bilingual, speaking both Japanese and English fluently, which proves useful for communication and diplomacy. His combination of sensory ability, combat skill, and calm analytical mind makes him one of the most reliable and versatile members of the Kingdom of Science.