One day when Tsukasa was young, he went to a beach to collect seashells, intending to use the shells to create a necklace as a gift to his infirm sister, as she loved tales of mermaid princesses.
While collecting seashells for Mirai, an old, drunk fisherman appeared and violently attacked Tsukasa to the point that his face became unrecognizable. The fisherman justified his assault on Tsukasa, claiming that he owned a fishing permit in the area and that Tsukasa's harvesting of seashells was trespassing. This event would greatly affect Tsukasa's view of humanity.
Sometime after this, Mirai became clinically brain dead, and as a result required constant life support. Unwilling to let his sister die, Tsukasa trained and became a top-tier fighter in the MMA in order to financially support his sister's medical care. His combat prowess eventually acquired him the nickname of "Strongest High School Primate", and made him famous enough to be known by even the likes of Taiju, someone who doesn't watch television.
Prior to the petrification, he made an appearance on a psychological magic show, he met the mentalist Gen Asagiri.
A schism forms between Senku and Tsukasa when the two are alone on the beach. Tsukasa tells Senku the story of how he was assaulted by a fisherman, when he had been collecting seashells for his sister before a surgery of hers. Following the conclusion of the story Tsukasa smashes a petrified man in the water, "killing" him.
Tsukasa explains to Senku his motivations; he believes that the petrifaction of the whole world is an opportunity for humanity to be cleansed, and for humanity to live in a natural utopia where only the "strong and pure" live, untainted by the corruption of modern technology. Tsukasa tries to turn Senku to his side, by arguing that they should only revive the innocent, young people of the world.
Senku, however, is wholeheartedly against this notion; Senku declares that, with the power of science, he will save all of humanity without exception — even those who Tsukasa considers evil.
Returning from his trip to harvest nitric acid for the revival of Yuzuriha, Taiju, oblivious to the events that unfolded while he was away, accidentally reveals to Tsukasa the vital component in the Revival Formula. After the three return to their shelter, Senku is forced to give up the location of the nitric acid water to Tsukasa in order to make time to revive Yuzuriha and make a plan against Tsukasa.
Tsukasa makes his way to the cave as directed, and deduces that the miracle ingredient in the cave water is nitric acid. Following this, Tsukasa quickly returns to the shelter. In his wake Tsukasa destroys many petrified humans, leaving a trail of rubble behind him. He returns earlier than expected, much to the shock of Senku.
Taiju realizes what Tsukasa did while he was gone when he sees the rubble of smashed, petrified humans in Tsukasa's hands. Senku sees that Taiju is about to start a fight with Tsukasa over the matter, and attempts to intervene by using a crossbow. Tsukasa, however, manages a superhuman feat; he catches the arrow loosed from the crossbow midair and sends it into the ground. He deals a strong kick towards Taiju's head, sending Taiju flying. Tsukasa is surprised to see Taiju still standing, but is even more surprised that Taiju hadn't tried to attack back. Realizing that Taiju would not fight to protect himself, Tsukasa threatens Yuzuriha, causing Taiju to faint. Tsukasa ends the quarrel and leaves the shelter, now an enemy of Senku, Taiju and Yuzuriha.
Tsukasa returns to the shelter sometime after Senku and company leave, and discovers that the group left the shelter hastily. This, combined with Senku's words regarding the uses of seashells, leads Tsukasa to the conclusion that Senku is planning on creating gunpowder in order to use it as a weapon against him. Tsukasa realizes that Senku will need sulfur in order to produce gunpowder — which can be found in abundance in the hot springs of Hakone.
Tsukasa quickly makes his way over to the hot springs, and finds Senku's location as a result of the smoke coming from the beacon fires he created. On the way to the fire, Tsukasa finds Yuzuriha and takes her hostage. Tsukasa confronts Senku with Yuzuriha in tow, threatening to kill her by placing his spear against her throat. Senku is forced to divulge the recipe for the petrifaction revival formula in order to save Yuzuriha's life.
Tsukasa gives Senku another chance to live — his life will be spared if he promises to cease all his efforts in progressing scientific development. Senku refuses again, telling Tsukasa that such a promise would be impossible for him to make. Following this adamant refusal, Tsukasa instantly kills Senku by crushing his cervical plexus. Yuzuriha and Taiju create a diversion using a rock and gunpowder, fleeing from Tsukasa with Senku's corpse.
As the explosion from the gunpowder settles, Tsukasa throws his burning clothes away. He concludes Taiju never intended to hurt him, simply creating a diversion so he could retrieve Senku's corpse and escape with Yuzuriha. He thinks to himself that it would be impossible for Senku to recover from the wound he inflicted since there's no professional medical help available
Now alone, Tsukasa notices someone following him, locates them and asks them who they are. As the stranger reveals themselves Tsukasa notes she is half-japanese and has blue eyes, asking himself whether Taiju juts revived her. He is then assaulted by the girl and makes a snarky remark about the rude greeting. The girl angrily says he will do his greetings in hell. After a brief clash, Tsukasa is amazed by her fighting prowess, having never heard of anyone that looks like her in the martial arts world. His opponent informs him she saw Tsukasa killing "the sorcerer gentleman" in exchange for saving Yuzuriha's life and states she will take no excuses. Tsukasa is surprised by the usage of the world sorcerer to which Kohaku replies that Senku summoned the mountain's wrath to combat him. He concludes that the girl isn't a modern timer and that she is a descendant of someone who depetrified in the past. He gets relieved, saying that he could kill the primitive group of villagers at any time and heads straight to the miracle cave as Taiju and Yuzuriha now know how to make gunpowder. In one go, he slices a tree that immobilizes Kohaku.
Tsukasa is shown to have amassed a great deal of physically powerful people at his side.
Tsukasa at some point revives Hyoga as well, a warrior renowned for his skill in spearmanship. The two supposedly agree on their ideologies of "culling" the current population as the world cannot hold all 7 billion people. Through Hyoga, Tsukasa learns that Gen's reports were forged and that Senku is alive and amassing the tools intended to defeat him.
Considering they need a significant portion of manpower to prepare them for the winter, in his coversation with Tsukasa, Hyoga adds that Senku's Ishigami Village is surrounded by water. Sieging the location even during the frozen waters in winter would require a wasteful supply chain. Tsukasa agres that the decisive battle is to be fought in the spring.
Hyoga inquires whether Taiju and Yuuzuriha should be allowed to roam freely. Tsukasa replies that they should be carefully monitored, but not cut off. The important thing is to keep the knowledge that Senku is alive hidden from them, in case they don't already know. Even if they are double agents, they have no means of conveying information to Senku.
Tsukasa states that what the group should focus on is a preemptive strike from the Kingdom of Science instead, as Hyoga replies that Homura is standing watch, albeit with an information delay too as there is no means of direct communication either on their side.
Later on, he pays respect to the fallen warriors who died at Ishigami village before discovering a phone was buried in the ground.
Tsukasa agrees to a ceasefire with the Kingdom of Science after Senku promises to depetrify his beloved sister, Mirai. Tsukasa is told because the stone formula can heal a wound, it should work for his sister. Tsukasa shows the location and finds his sister's statue. Senku poured the formula on her and Mirai was revived while awakening from her coma. Happy at seeing her, Tsukasa embraced his sister.
Their peace is short-lived, however; he is soon betrayed by Hyoga. Hyoga attempts to kill Mirai but Tsukasa takes the hit. Tsukasa and Senku defeat Hyoga, he is critically injured and put into cryosleep.
Senku plans to return to Ishigami village to petrify and then de-petrify the frozen Tsukasa, with the petrification device onto his body together with Mirai and other Kingdom of Science team. Tsukasa is then happily reunited with his sister again. Tsukasa is approached by the new addition Matsukaze, who is curious about his skill and challenges Tsukasa to a sparring match. Tsukasa accepts and easily bested by his opponent who is in awe at the feat, while surrendering. Tsukasa notes that Matsukaze might be a real challenge in the future. At Gen's request, Tsukasa joins the others in recreating his scars with paint to commemorate his loyalty to Senku.
As preparations for the global voyage are ongoing, Tsukasa expresses his appreciation of Gen, who demures, claiming he only takes advantage of other people’s skills. When concerns arise about the potential for corrupt individuals to be revived during their journey, Tsukasa reassures his allies that he won’t allow villains to ruin their plans. When Ryusui mentions a prize of Dragos for spotting land first, Tsukasa expresses confusion, before Minami rushes Ryusui away. Tsukasa seems to overhear Ryusui’s conversation with Minami about the positives of money.
Later, after the Perseus sets out to sea, Tsukasa is interviewed by Minami, and he states his intent to protect the integrity of science from the schemes of corrupt people and guns. During the poker game between Ryusui and Senku, Tsukasa comments to Chrome that Kohaku took Senku’s replacement cards from the middle of the deck. After the game, Tsukasa dresses in new clothes made by Yuzuriha, and receives a custom mocktail made by Francois.
After the party ends, Tsukasa was sullen at hearing Matsukaze's past before an inebriated Matsukaze requested that he trained him. Although Matsukaze apologized for overstepping, Tsukasa decided to start weapons training for the crew’s fighters. To this end, he asked Senku to revive Hyoga, believing that he was better suited to teach the warrior weapons. Hyoga agreed but requested that other fighters be revived and soon they started training aboard the Perseus.
Very soon, the ship reached land and Tsukasa was pleased with this.
When the Perseus arrives in San Francisco, the warrior team follows the exploration crew. Soon alligators attack, though Tsukasa was pleased because of the dwindling supplies. With that he and the other warriors defeat the beasts, they soon use the Alligator meat to restock on supplies. Tsukasa is exceptionally pleased with the hamburgers that François made from them. Tsukasa then shows one of the Alligators had swallowed an ear of corn and Senku realized gathering corn might be in grasp. 
They continue to find corn that has been scattered through the river. That night, the crew set camp before Tsukasa note on an eerie feeling. He smells smoke from a gun and alerts everyone to retreat inside the boat, where they could take cover. Surely enough, bullets rain down and Tsukasa ducks for cover in the lab. After the gun stops shooting, Ryusui has the group enter the boats before fleeing the scene. 
The group escape on the river, but hears an engine, before Tsukasa is shocked to witness an aircraft flying above them, staring at it in awe. Fortunately, Senku comes up with a plan and has Kirisame bring the plane down with a substance, as the pilot escapes. Senku has the plane salvaged, wanting to use it in the future while Ryusui supports this plan.
With the enemy temporarily held off, Tsukasa tells the group that it is most likely they will fall back to strategize. Tsukasa watched as Senku sent Gen, Chrome, and Kohaku to scout the forest for the enemy.
When the crew get a call from Chrome and Kohaku, Tsukasa told them to minimize the conversation because the enemy might be monitoring their frequency. He watches Senku hang it up because the enemy might track them. Surely enough, the enemy Dr. Xeno makes contact, with Tsukasa shocked by this even more so when he requests to speak with "Dr. Taiju". Tsukasa hears Senku realize this was a ruse to protect him from harm. Once Taiju refused Xeno's offer of servitude at the urging of the others, Tsukasa heard a noise and was shocked to spot another plane flying above the Perseus. He notes how the enemy is taking a new strategy by flying above them. He watches Senku prepares a new tactic, as he announces to the crew that he and Kaseki are building a runway for the Perseus. 
Tsukasa then calls a meeting, having an artist draw a diagram of the present situation. He and Senku agree on sending a small group to capture Xeno to have a chance of defeating the enemy. Tsukasa, Hyoga, Ukyo, and Suika then set out into enemy territory.