Tsukasa Shishio first emerged as a formidable high school martial artist, celebrated as the "Strongest High School Primate" prior to the global petrification. His childhood trauma—an assault by an intoxicated fisherman while collecting seashells for a mermaid-themed necklace for his sister Mirai—fueled his deep distrust of adult authority and societal systems. When Mirai entered a coma from an incurable brain disease, Tsukasa turned professional in mixed martial arts to finance her care, condemning the pre-petrification healthcare system as exploitative. Revived by Senku Ishigami to counter a lion attack, Tsukasa initially aided Senku and Taiju through hunting and protection. He soon unveiled his radical ideology: opposing the restoration of modern civilization, which he viewed as inherently corrupt. Advocating for a world exclusively of morally upright, physically strong youth, he shattered petrified statues of adults deemed irredeemable—an act Senku condemned as murder. Tsukasa framed this as necessary purification, though he spared defiant individuals like Chrome, revealing a capacity for mercy. Seizing the revival formula, Tsukasa established the Empire of Might. He selectively revived warriors like Hyoga and Homura to forge a militaristic society, strategically monitoring threats such as Taiju and Yuzuriha while planning preemptive strikes against Senku’s Kingdom of Science. His tactical brilliance surfaced when he intercepted Senku at a sulfur source, anticipating gunpowder production. In combat, Tsukasa demonstrated superhuman prowess: killing lions barehanded, snatching crossbow bolts mid-flight at 200 km/h, and felling trees with single strikes. His MMA-honed skills overwhelmed adversaries, including Kohaku and later American soldiers. The Stone Wars pivoted when Senku proposed healing Mirai using petrification’s restorative properties. Tsukasa accepted a truce; Mirai’s recovery from brain death tempered his resolve. He then sacrificed himself to shield her from Hyoga’s betrayal, sustaining a fatal lung wound. Senku devised a cryogenic solution: Tsukasa would be killed, frozen, and later depetrified to heal. Accepting the irony of Senku "killing" him twice, Tsukasa embraced the plan. Post-revival, he abandoned his purist ideals, joining the Kingdom of Science to atone. His role evolved to protecting Senku’s projects and leading combat units against threats, including the American colony. He committed to preventing corruption in the new civilization, eventually journeying to the moon to confront petrification’s origin. After revival, Tsukasa retained his physical dominance but adopted collaboration. He reconciled with former foes, respected Ryusui Nanami’s economic principles, and mentored fighters like Matsukaze. His depetrification-healed scars were deliberately repainted as symbols of loyalty to Senku’s mission.