Yô Uei was a police officer before the global petrification event, known for using excessive force against fleeing suspects and routinely disregarding regulations. This conduct resulted in professional consequences and limited career advancement. Petrified mid-act of urinating on a wall, he was later revived by Tsukasa Shishio. Uei joined the Empire of Might as an enforcer. During the Stone Wars, he guarded Chrome but underestimated him as primitive, leading to Chrome's escape. Fearing punishment for this failure, Uei faked his death and fled. While hiding, he encountered Homura Momiji near Ishigami Village and agreed to free her in exchange for benefits, subsequently contacting her ally Hyoga. Returning to the Tsukasa Empire after Tsukasa's defeat, he found it merged with the Kingdom of Science. To integrate, he falsely claimed amnesia and assisted Yuzuriha in reconstructing petrified statues. He participated in Kingdom projects like shipbuilding contests, where his poorly built raft stood out against others' designs, and hot air balloon construction, frequently arguing with Magma over modern versus primitive techniques. Uei also joined farming efforts under Taiju, initially failing until applying scientific soil treatments. On the Treasure Island expedition, Kirisame petrified him and dumped him into the bay. After retrieval and revival, Senku entrusted him with a firearm due to his police background. Despite initial inaccuracy and showing off, he practiced diligently with Amaryllis's help. In the battle against Ibara, he missed a critical shot at Moz but later disarmed Ibara by shooting the petrification device from his hand. Ibara almost immediately re-petrified him; he was revived again later. During later missions aboard the Perseus to America, Uei gambled and complained about the lack of alcohol until beer was recreated. He fought alligators and Stanley Snyder's forces, firing at an attacking plane despite skepticism. Magma easily persuaded him into risky plans, though Nikki prevented them. Uei remained in Corn City with a subgroup after a truce. In South America, he helped create synthetic diamonds and fought American soldiers to secure the petrification device. Critically wounded by gunfire, he advanced under Nikki's encouragement until the Why-Man's signal caused his re-petrification. After a nine-year stasis, he revived in San Francisco and contributed to constructing a computer, initially resisting the labor but motivated by financial rewards. He assisted in global supply missions, delivering corn to Australia and farming rice in Indonesia without complaint. Returning to Japan, he noted village productivity, fed Suika's pets, and joined a celebration feast. His personality blends arrogance, laziness, and cowardice with moments of loyalty and dedication. He constantly competes with Magma, bickers over trivialities, and seeks status, yet showed care for subordinates by redirecting blame during his desertion. Uei adapted to Kingdom life, expressing genuine amazement at Senku's inventions and regret at not meeting him earlier. His skills include tonfa combat, running, and marksmanship requiring practice. He consistently wears a stone fragment over his right eye, despite occasionally losing it. Post-series, he helped establish a new police force.