Kaseki (カセキ) is the artisan of Ishigami Village. With expert skill and precision formed by his numerous years of experience as a craftsman, he is a key member of the Kingdom of Science, responsible for creating many of their scientific inventions.
Kaseki is a bald, short, old man with a large, white beard. Although initially appearing to be frail, when fired up, he bursts through his clothes, revealing a muscular body, likely honed by his years working as a craftsman.
Kaseki is an honest older man who is prideful in his work and skill as an artisan. Unassuming unless provoked, he displays boundless energy when excited about his work.
Originally wary of Senku, Kaseki quickly becomes a loyal and prominent member of the Kingdom of Science. His love for crafting since his childhood helps him form strong bonds with advocates of science. Having been relatively isolated for much of his life due to his interests, he now considers Senku and Chrome as close friends, despite their age differences. He is alike to them in the fact Kaseki is passionate about his craft and despairs when it fails.
A genius craftsman, Kaseki picks up techniques with little effort. Upon seeing glass for the first time, he immediately understood how to work best with the material.
As one of the oldest members of the Kingdom of Science, Kaseki is relatively wise. He often imparts wisdom on the other members, and is unafraid to admit his own shortcomings.
Despite his pride, Kaseki often seeks external validation for his work, particularly from women.
Abilities and Skills
Master Artisan: Kaseki is an master artisan with over fifty years of experience. He designed and built much of Ishigami Village, including the island's bridges. He also made Kohaku's shield, originally for her father Kokuyo as a reward for winning the village tournament and becoming chieftain.
Kaseki picks up new techniques extremely quickly, inherently understanding how to use materials he's never seen before. He can craft objects solely from Senku's diagrams with little practice. He's even able to create extremely complex structures, including engines and vacuum tubes. Senku admits Kaseki's skills far surpass his own.
Intelligence: Along with Chrome, Kaseki is one of the original two members of Ishigami Village with scientific knowledge. He's shown to be extremely knowledgeable, particularly about crafting techniques.
Physical Abilities: Kaseki's physical abilities are high, despite his old age, due to his physically-demanding work, and they were further heightened after Kaseki was revived thanks to the healing properties of the petrifaction process. He is strong enough to tear through rope. However, he has limited combat experience.
Just like the rest of the village, Kaseki is a primitive human. Kaseki is also a descendant of Byakuya Ishigami and his crew. In his youth, Kaseki loved crafting all manner of creation. However, this made the other villagers look at him with disdain as a result. Kaseki built the bridges that connect the Ishigami Village and started creating shields for the tribe.
Kaseki is introduced as one of the inhabitants of Ishigami Village. Upon hearing rumors of Senku, a boy from outside the village, he found it curious.
In order to create glass vessel, Chrome solicited Kaseki's assistance, tying him up and dragging him back to Senku. The old man at first refused to help them due to his treatment, but became intrigued by their attempts at glass work. When Senku and Chrome attempted to amateurishly blow glass and fail, it infuriated him to the point that he broke through his bonds and took over the process.
Along with Chrome, Kohaku and Suika, Kaseki aids Senku in making gas masks in order to acquire an antibiotic for Ruri.
Ginro tries to rationalize his lack of help in gathering sulfuric acid, saying that it's a given he would be scared since there's a risk of death. He criticizes them for being reckless while posing as being brave. Kaseki interrupts him by saying he's showing his own weakness by running away and saying nothing, then painting them in a bad light over it.
As Ginro tries to protest, Kaseki tells Ginro that he's not weak at all - fear being a key feeling for survival. The former adds that every human feels fear deep inside. Kinro who has a blurry disease is about to fight Magma, and Kaseki says he surely must feel fear. However, with a reason and for the sake of what's precious, someone can eventually beat that feeling of fear. Kaseki intentionally leaves the additional gas mask for Ginro.
Kaseki plays a crucial role in village games as he suggests winning over the village tournament to acquire alcohol to Senku, prompting the latter to join himself.
Kaseki comments on Ginro's selfish attempt to win the village games himself after misunderstanding Ruri's formal statement that she is indifferent about marrying the winner of the competition. He states that Ginro is even worse than Magma since he has no ill intent behind his actions.
Once Senku defeats Ginro by using Suika's helmet as a fulcrum for his spear and hitting him in the groin with the other end, Chrome faints in the next round and Senku is crowned the winner of the bout. Once the latter gets hold of alcohol, he immediately divorces Ruri and snatches Kaseki so they continue working on the cure. He shows of a spinning bamboo structure he made to the group, wanting girls to praise him. Instead, he gets praised by Senku, much to his chagrin. When asked about its utility by Gen, Kaseki says he has no idea what it could be used for.
After Senku tells Kaseki to look forward to tomorrow and leaves, Kaseki grabs Gen and orders him to watch the creation along with him so he doesn't get lonely. As Gen protests, he accidentally rips Kaseki's clothes and reveals his muscle, prompting Gen to comply.
Once Ruri is finally cured, Kaseki comments on her immediate tomboyishness upon recovery, concluding it must run in the family.
As Suika arrives to the battle between Kinro and Magma, Kaseki is relieved to see that she is well.
After Senku became the village head, Kaseki helped in the advancement of the people in his ways. For the village's advancement, Senku, along with Kaseki, start forging Japanese swords for all their warriors. Senku explains how the task of making these swords is very difficult and tedious, but Kaseki easily learns it. Kaseki was able to make enough swords to equip every capable fighter in the village.
Once the village is set ablaze, Kaseki worries about the spread of the fire. As Suika leads the invaders away from the village, she is congratulated by Kokuyo and scolded by Kaseki for her recklessness.
The craftsman marvels at the possible creation of a cellphone, its properties and its usage as a wartime communication device. He enthusiastically observes the schematics for its making along with Chrome. Senku briefly explains how the voice's small output of electricity is amplified by the cellphone, creating electromagnetic waves which are then received on the other end. The craftsman shares the joy of eating cotton candy made by Senku alongside the rest of the village.  Kaseki, along with Chrome, spends three days to build a water wheel/mill. Senku knew about the invention, but is nonetheless greatly surprised the two have achieved such level of craftsmanship without possessing any prior knowledge. The water wheel was then used, along with the cotton candy tool, to create an electrical water powered generator.
The craftsman club is getting worn by Senku more and more, with Kaseki and Chrome complaining about the amount of workload imposed onto them. Together with Senku, the duo learns about the functioning of gears, making batteries along the way. Kaseki notes that while before he was lazing around in the village, ever since Senku arrived, things have gotten more interesting and fun. The old craftsman states most of the village feels the same way. When the record player is made, Kaseki is amazed to hear the recording of Senku's father, the founder of the village. He is left in awe at the song of Lillian Weinberg.
He aids in making a tank to attack Tsukasa's forces.
He later aids Senku in freezing Tsukasa to save his life.
Kaseki aids in building cameras and a hot air balloon. He makes a car to travel. Kaseki aids in building the Perseus and finishes it in a year. He joins the Perseus as part of the crew.
He is rescued by Taiju, Ryusui, and Soyuz and is the third member of the Kingdom of Science to be depetrified. Kaseki is excited at witnessing petrification and his rejuvenated body before he is disappointed at the state of his vehicle. He is recruited to help Senku make a drone.
He and Ryusui notice Chrome and asks what his plan is, after he starts to dash ahead.
He is later repetrified by Ibara but not before playing his part in Chrome's plan.
After the battle, he is later depetrified again to repair the Perseus. He along with the others revive their friends. When Whyman attempts to petrify them but fail, Kaseki is shocked to hear that he sounds like Senku.
Kaseki is later seen remarking on Chrome's speculation of the Whyman, bringing up the matter on why the Petrification Weapon was on the island. After a new warrior was revived, Kaseki is seen running with Chrome, Ryusui, and Senku back to the ship. He asks Ukyo if the signal of the enemy is nearby and Senku reveals he is on the moon.
As the Perseus sets sail to return home, Kaseki questions whether the ship will be huge and Senku tells him that they will travel the world to gather materials suitable for space travel. 
Working with Yuzuriha, the two are tasked with creating a globe. The two recall Senku's remarks and feeling energized at his audacity, they create a massive diagram, complete with cities. Seeing this unbelievable display, Senku remarked they went overboard.
He is very excited to reach land.
Kaseki is later excited at the thought of modifying the enemy aircraft, once the others are worried after learning they had a second one. He and Senku also decide to build a runway for the ship.
While working on the ship, he joins the discussion of Luna with Senku and Ryusui. He remarks on Senku's logical way of dealing with her. He is later seen excited by the recreation of ice cream. After Senku expresses familiarity with Zeno, Kaseki wonders how Senku knows him.
He finds Senku's stories about science amazing and eagerly builds the invention. He respects Senku as his new chief and a person while Senku values his capabilities.
Kaseki is on good terms with Chrome due to their similar interests in science, craftsmanship, and material gathering. The two often work together on projects like glass and vehicles.
He has been said to have a soft spot for Gen. When the Kingdom of Science splits into different groups for a project, Kaseki almost always takes Gen aside to work with him. Kaseki is the only person who can force Gen, who is normally able to outwit anyone, into helping him (mostly because Gen is intimidated by the old man's physique).
While the two don't have too much interaction together, the two get along well as fellow artisans. Both are close to Senku and often help him create his more complicated and intricate inventions. Kaseki helps build her a loom and is saddened when he believes it was not what she wanted. Similarly, when Senku assigned them the task of building a 3d model of the Earth based on his plans, he claimed it was fine for it to be sloppy but both Yuzuriha and Kaseki got angered by his remark, saying that as fellow craftsmen they could not allow their work to be poorly handled and both shared the same level of satisfaction and excitement at its completion.
- His name Kaseki is the Japanese word for Fossil.
- This seems to be a joke about his age.
- Kaseki has a habit of ripping apart his clothes when excited, even while wearing difficult-to-produce clothing crafted by Yuzuriha.
- He ranked 9th in the 1st popularity poll and 14th in the second poll.
|Male||Taiju Oki • Senku Ishigami • Gen Asagiri • Chrome • Kaseki • Kinro • Ginro • Magma • Kokuyo • Ryusui Nanami • Matsukaze • Tsukasa Shishio • Hyoga • Mozu|
|Female||Yuzuriha Ogawa • Ruri • Kohaku • Suika • Nikki Hanada • Minami Hokutozai • Kirisame • Homura Momiji|
|Male||Chrome • Ginro • Jasper • Kaseki • Kokuyo • Kinro • Magma • Mantle • Soyuz • Tetsuken • Ibara • Mozu • Oarashi • Matsukaze|
|Female||Garnet • Kohaku • Ruby • Ruri • Sapphire • Suika • Shirogane • Shovel • Turquoise • Amaryllis • Kirisame|