Tsukasa Shishio first emerges as the "Strongest High School Primate," commanding extraordinary physical strength, speed, and combat skill. He kills a lion with one punch, catches crossbow bolts traveling 200 km/h, and swiftly overpowers multiple opponents. Years of dominating mixed martial arts competitions forged his martial prowess, augmented by enhanced senses detecting bloodlust or faint smoke. Yet he acknowledges vulnerability to threats like the Amazon rainforest or Stanley Snyder. A traumatic childhood incident shaped his worldview: a drunk fisherman assaulted him for collecting seashells on a private beach—shells intended for a necklace for his younger sister Mirai, who adored mermaid tales. Mirai later fell into a coma from an incurable brain disease, cementing his distrust of adults and societal structures. To fund her medical care, he pursued mixed martial arts, gaining fame and wealth but witnessing pervasive corruption and inequality, particularly in healthcare. Petrified for 3,700 years and revived by Senku Ishigami, Tsukasa initially aided Senku and Taiju with protection and sustenance. He soon revealed his ideology: viewing the petrification as a chance to cleanse humanity. He planned to revive only young, morally pure individuals and destroy statues of the corrupt, especially older adults, believing this would prevent a resurgence of a society tainted by greed, weapons technology, and exploitation. This philosophy clashed directly with Senku's goal to revive all humanity and rebuild science, making Tsukasa declare Senku his enemy. To achieve his vision, Tsukasa founded the Empire of Might, reviving strong warriors like Hyoga and Homura. He employed ruthless tactics: taking Yuzuriha hostage to extract the revival formula and smashing statues to eliminate threats. He seemingly killed Senku by targeting his cervical nerve, though Senku survived via preemptive measures. Tsukasa's forces clashed with the Kingdom of Science in the Stone Wars, reaching a stalemate at the Miracle Cave. Senku leveraged nitroglycerin explosives to force negotiations, offering a truce: peace in exchange for depetrifying and healing Mirai using the petrification's restorative properties, potentially curing her brain death. Tsukasa accepted. Mirai revived and recovered. During this fragile peace, Hyoga—Tsukasa's former ally—betrayed him, attempting to assassinate Mirai. Tsukasa intercepted the attack, sustaining a fatal lung injury. With no means to save him, Senku proposed cryogenically preserving his body until petrification technology could heal him. Tsukasa consented, and Senku euthanized him. After the Kingdom acquired the petrification device, Tsukasa was depetrified, fully recovered, and reunited with Mirai. Revived, Tsukasa allied with the Kingdom of Science. He shifted his ideals, now striving to ensure Senku's scientific world would not repeat past corruptions, particularly the exploitation of the innocent. He joined expeditions, traversing the Amazon and preparing for a moon mission to confront the petrification source. His combat skills remained vital, sparring with warriors like Matsukaze and defending allies. He adopted symbolic gestures, redrawing his scars with paint to signify loyalty to the Kingdom. Tsukasa balances violent capability with careful calculation. Initially a calm idealist, he displayed ruthlessness pursuing his goals but adhered to a personal code: respecting nature (utilizing hunted lions fully) and minimizing suffering during kills. Despite animosity toward Senku's methods, he acknowledged Senku's superior intellect and regretted they couldn't have been friends earlier. Post-redemption, he exhibited greater restraint, forgiving former adversaries like Hyoga and embracing a protective role within the Kingdom.