Tsukasa Shishio, dubbed "The Strongest Primate High Schooler," boasts exceptional physical prowess, standing 195 cm (6'4") with a muscular build and distinctive stone markings. Before the global petrification, he dominated the UFC as a teenage mixed martial arts champion. His combat mastery stemmed from relentless training to support his younger sister, Mirai Shishio, who required life-sustaining care due to a coma and brain death. A formative childhood incident on a beach, where a drunk fisherman assaulted him for collecting seashells to make a necklace for Mirai, fostered his deep resentment of adult authority and societal hierarchies. Revived by Senku Ishigami to counter a lion attack, Tsukasa initially aided Senku and Taiju Oki with food and protection. He soon unveiled his vision for the stone world: a utopia exclusively for the young and morally pure, free from the corruption and technology of the past era. Clashing with Senku's goal of reviving all humanity, Tsukasa believed it would perpetuate old societal ills. To achieve his ideal, he systematically shattered petrified statues of adults and those he deemed "impure," viewing this selective destruction as necessary purification. This ideological split drove him to seize the revival formula, take Yuzuriha Ogawa hostage, and deliver a near-fatal blow to Senku's cervical plexus. Establishing the Empire of Might, Tsukasa revived physically strong followers like Hyoga and Homura to forge a militarized society. He permitted Taiju and Yuzuriha to join under surveillance as potential spies. His regime enforced a primitive existence without advanced technology, though it tolerated basic tools. During the Stone Wars, Tsukasa confronted Senku's Kingdom of Science but surrendered upon witnessing the destructive power of nitroglycerin-based weapons. He agreed to a truce when Senku proposed reviving Mirai, leveraging petrification's potential to heal her brain death. Mirai's successful restoration became a turning point, marked by Tsukasa embracing his sister joyfully. Hyoga's betrayal during the truce saw Tsukasa intercept a spear thrust meant for Mirai, sustaining a fatal lung injury. With no means to treat the wound, Senku proposed a plan: fatally injure Tsukasa, preserve his body cryogenically, and later use the petrification device to heal him. Tsukasa consented, acknowledging the irony of Senku "killing" him a second time. Following preservation, he was depetrified using the Medusa device, making a full recovery. This experience cemented his loyalty to Senku's mission. Post-revival, Tsukasa joined the Kingdom of Science, channeling his ideals toward preventing corruption within the emerging scientific civilization. He accompanied the crew to the United States, contributing his combat skills to expeditions like hunting alligators in the Amazon. While retaining his desire for a morally pure society, he abandoned enforcing it through violence or suppressing technology. He expressed respect for Ryusui Nanami's economic philosophy, seeing currency as a tool to unite rather than control people. Tsukasa also sparred with allies like Matsukaze, recognizing their potential with modern fighting techniques. His abilities encompass superhuman strength—killing lions and alligators with single strikes—and speed, demonstrated by catching crossbow bolts traveling at 200 km/h. He combines mastery of multiple martial arts with acute senses, detecting threats like gunpowder smoke or concealed enemies. Despite his physical dominance, he acknowledges limitations, such as the dangers of the Amazon rainforest or opponents like Stanley Snyder. Intellectually, Tsukasa deduced scientific plans like Senku's gunpowder production and replicated complex formulas after minimal instruction, with Senku noting he would have academically rivaled Chrome in a school setting.