Tsukasa Shishio earned the title "Strongest High School Primate" through extraordinary physical prowess, including lethal one-punch strength and reflexes enabling him to catch crossbow bolts at 200 km/h. His combat expertise spans mixed martial arts and primitive weapons like stone blades. Coupled with high intelligence, he deduces complex concepts such as nitric acid's depetrification properties and identifies threats like gunpowder production. Born in 2001, Tsukasa devoted himself to fighting to fund life support for his younger sister Mirai, left brain-dead at age six. A childhood assault by adults while collecting seashells for her cemented his contempt for adult authority and societal hierarchies, which he deemed inherently corrupt. Revived after global petrification by Senku Ishigami and Taiju Oki, Tsukasa initially aided them before unveiling his plan to forge a "pure" world. He founded the anarcho-primitivist "Empire of Might," reviving only morally untainted youths while destroying adult statues. The empire enforced Social Darwinist principles, prioritizing physical strength and rejecting technology to prevent corruption. His conflict with Senku’s Kingdom of Science paused when Senku offered to depetrify and heal Mirai using petrification’s restorative effects. After Mirai’s revival, Tsukasa was betrayed and mortally wounded by lieutenant Hyoga. To save him, Senku fatally injured Tsukasa and preserved his body in cryosleep for future healing. Following revival via petrification device, Tsukasa allied with the Kingdom of Science. He supports rebuilding civilization but vigilantly opposes exploitation, emphasizing this during expeditions like the Amazon voyage. Standing 195 cm with a muscular build, Tsukasa has wild brown hair, swollen knuckles from combat, and stone markings across his face and torso. He initially wore a lion pelt but adopted practical gear like rubber boots later. Personality merges violence with rationality, adhering to codes like honoring hunted animals. Though he destroyed statues, he remembered each victim, revealing internal conflict. Post-revival, he softened, forgiving former enemies and focusing on safeguarding Senku’s vision.