Relationships
Family
Byakuya Ishigami
Senku and his adoptive father's relationship was complex. However, they got along with Byakuya encouraging him to pursue his goals of science and Senku helping Byakuya be an astronaut. In the thousands of years after the petrification, Senku discovered his father created the Ishigami village and told tales of him, for the stories to reach Senku after his release. Although Senku hardly shows affections, he secretly cared for his father and was sad that while he survived the petrification, he died sometime after and was pleased his father held such faith in him. Above even their mutual love of science, discovery, and pushing the limits of humanity's potential, Senku and Byakuya shared a critical trait: their belief in fun being crucial to humanity in all its forms: music, manga, movies, games, literature, and more. The two were always smiling in the midst of a difficult venture and found the thrill of a challenge exhilarating. The ability to find the joy in even crucial tasks where lives were at stake was part of what allowed both of them to withstand the trials and tribulations they faced in their steps towards restoring civilization.
Kingdom of Science
Taiju
Taiju and Senku have been friends since childhood. In the past, Senku was protected by Taiju from bullies. This led Senku to develop a deep sense of respect and trust towards Taiju even though he is an airhead. When Senku was depetrified, he did everything he could to survive but admitted he needed Taiju and his endurance to overcome the obstacles to come. Taiju later became a main unit in Senku's plans to expand the Kingdom of Science, his strength and endurance proving vital to the Power Team.
While the two are pretty much polar opposites in pretty much every way, they are very similar in that they are both very resilient in the face of adversity. Taiju has an unconditional trust in Senku despite not being able to understand the majority of his friend's plans, but manages to contribute with bouts of insight and his enormous strength of will.
Yuzuriha
Yuzuriha and Senku are friends through Taiju, Senku knows how deeply Taiju loves Yuzuriha and respects his friend's love interest. He is even willing to sacrifice himself to protect her and abandons the depetrification formula to Tsusaka. She possesses a genuine ability for tailoring which is useful for the Kingdom of Science. He also has her use her sewing skills to fix broken petrified humans.
Kohaku
Kohaku sees Senku as a gentleman and she is rather impressed by him. She first saw him sacrificing himself to save Yuzuriha and since that moment, she admitted that she was very interested in him. She led him to the Ishigami Village where Senku met all the other villagers. She did not trust in Senku at first but, over the course of their adventures, she accepts him and trusts him with very important things, like Ruri's life. Also, she may consider him a very close friend as she is not very offended when Senku calls her a Lioness and especially a gorilla, and even admits to him that she finds him physically attractive. In turn, Senku greatly relies on her due to her physical strength and skill as a fighter. She often helps him in his scientific endeavor gathering material or lending her physical power. Though he enjoys teasing her by calling her lioness or gorilla (which she hates), he genuinely cares for her as a close ally and friend and trusts her abilities, as shown in the Treasure Island, where he has her spy on the tribe by entering into the harem and the two manage to communicate their plans and deliver materials to each other in secret.
Chrome
At first, Senku and Chrome had a rivalry. Chrome proclaimed to be a genius sorcerer and Senku claimed to be a scientist. Chrome showed off his skill to impress Senku, Koharu, Kinrou, and Ginrou but was completely overwhelmed when Senku revealed that he knew all of his tricks. Nonetheless, Senku was impressed by all the knowledge that Chrome had learned all by himself. In a way, he reminded Senku of himself. After a small duel between the two, Chrome loses to Senku and joins his Kingdom of Science. They then team up to overcome the challenges towards creating the cure-all for Ruri. Chrome eventually assist Senku in many ways, including discovering the Ore Deposit that the Kingdom of Science needed for their campaign.
Senku entrusts Chrome with restoring science if he dies.
Gen Asagiri
A twisted mentalist. Originally sent by Tsukasa as a spy, later defected to work with Senku. Realizing that he can revive science, Gen becomes one of the most trusted retainers to manipulate others and advance Senku's plans. Senku himself has no problems with Gen being a turncoat and becomes close friends with Gen. The two are both intellectual equals, though Gen is more talented in the science of psychology and the art of of manipulation and lacks in most fields of physical scientific knowledge. He assists Senku by manipulating people into following Senku's orders, facilitating cooperation, and helping Senku prepare for the bloodless war against Tsukasa. While Gen initially claims he joined Senku's army for the benefits, he later admitted he had seen Senku write his birthday and name on a stone and became fascinated with the person who could not only know the year and time they were de-petrified but also swore to bring back science, telling Senku he already liked him a lot before they met. He even goes so far as to have the Ishigami village help him build a telescope for Senku's birthday. Senku himself greatly trusts Gen with his plans and the two enjoy scheming together such as tricking Ryusui into buying lots of items such as clothes and sportswear so they would have funds to buy oil from him. Gen is frequently amazed by Senku's inventions often acting as the straight man to the many amazing scientific developments Senku accomplishes and holds great faith in him. In turn, Senku acknowledges Gen as not being completely devoid of a moral compass despite Gen claiming to be the most shallow man he'll ever meet.
Suika
Suika first met Senku while he, Chrome, and Kohaku were gathering black sand in the nearby river. She wanted to help them as she was often ridiculed and was never of help to others. She immediately becomes attached to Senku after he did not ridicule her for wearing a melon on her head or ask her about it (though Kohaku and Chrome point out he more likely didn't care). He was genuinely impressed by her stealth and ability to hide and gather information, employing her to find out what the villagers liked so he could use science to bait them to his side. Later, as thanks, he makes glasses for her when he learns she wears the melon rind to see better (as she is nearsighted and the pinhole effect of wearing the melon helps her see). He ensures the first thing she sees are sunflowers and she becomes one of his most loyal friends, often helping him gather information and assisting in his labor-intensive work. He shows a good deal of trust in her abilities along with care for her. When she befriends a pig, she worries Francois will cook it and Senku implicitly asks Francois to allow her the pig as a pet. He similarly trusted her to help bring the lab to him when she was the only one not petrified by the Treasure Island Tribe who boarded and took the items of the ship.
Kaseki
Senku constantly works with Kaseki in restoring science and making weapons and materials. Kaseki did not trust Senku at first, but the two formed a bond over their love of building items and vehicles. When Kaseki and the others are petrified, Senku planned to revive Kaseki first but had to change plans after Kaseki is thrown into the ocean.
Ryusui Nanami
The child of the owner of Nanami Conglomerate. Despite his twisted personality, Senku and Gen's tag team is able to outwit the sailor, much to Ryusui's shock. Together, they team up to search Sagara Oil Fields that have been discovered by Kohaku and preparing for a journey in a search of the source of petrification.
Ryusui mentions that had they met in the pre-petrification world, Ryusui would have hired Senku for his company.
Ukyo
Former SDF Navy that serves as a submarine operator. He joins Senku after learning he and Yuzuriha are repairing the broken petrified humans. He becomes one of the vital assets for Science of Kingdom due to his perk of superhuman hearing.
Former Enemies
Tsukasa
Since his depetrification, Senku was always wary of Tsukasa and his goals. Because he was too strong, Senku had no other choice but to consider the possibility of Tsukasa and him not sharing the same principals. Tsukasa however deeply respects Senku and asks him to abandon science so that he doesn't have to kill him. Tsukasa then shares his regrets of not having talked to Senku 3700 years ago, saying that he may have become his very first friend, to which Senku replies ''probably''. The two remain, enemies, as Tsukasa's troops frequently try and fail to destroy Ishigami village. However, Senku manages to order a ceasefire with Tsukasa upon revealing he could not only help de-petrify Tsukasa's sister but also cure her of her brain dead vegetative state. When he does so, Tsukasa is grateful and promises not to harm Senku's group again. He even goes so far as to protect him from Hyoga's attack and trusts in Senku's promise to save him and cryogenically freeze him until he can.
Despite their ideological differences, Tsukasa and Senku respect one another for their intelligence and strength of will.
Hyoga
Hyoga and Senku first meet as Senku manages to create Japanese Katana for The Kingdom of Science uses. Senku bravely asked Hyoga to tell Tsukasa that Senku is still alive, thus invalidate Gen earlier claims. After the battle to claim the Miracle Cave ended up with a truce, in exchange for reviving Mirai, Hyoga backstabbed Tsukasa by stabbing him in his lungs, with Senku follows soon after. Thanks to Tsukasa and Senku's joint effort, Hyoga is finally defeated and keeps imprisoned on Perseus. Later, during the attack of the petrification kingdom, Hyoga was revived as Senku's last-ditch effort. In the end, Hyoga decides to help Senku in battling Mozu, and defeated him.
Antagonistic
Homura
He believes he can turn her over to their side despite her strong loyalty to Hyoga. He gives her cotton candy claiming he wants to sweeten her up though Ruri suggests it was actually because she was a lone girl in enemy territory and he wanted to comfort her. Senku uses the blue jewel powder to track her. When she and Hyoga are captured, he keeps the both of them as prisoners rather than kill them. When they set out on a voyage, to ensure they don't attack the village while he and the main team are gone and in case of needing extra muscle he forcibly brings her and Hyoga along.
Enemies
Whyman
Whyman is the nickname given to a mysterious individual whom they received a Morse code message from. Senku believes them to be the individual responsible for the petrification incident, or at least related to it somehow. One of the reasons Senku built the Perseus was to find out who Whyman is.
Minister Ibara
Ibara is the current leader of the petrification kingdom and currently, the one who held Medusa, the source of Petrification. He petrified many of Senku's allies.
Mozu
Mozu initially is about to kill Senku and the Kingdom of Science members after Kirisame petrifies Ginrou and Kohaku. However, thanks to Gen psychological abilities, they temporarily form a truce to kill Ibara instead and claim Medusa. Mozu quickly betrays the kingdom of science after Ibara manages to find out about Senku's plan.
Kirisame
Kirisame petrified many of Senku's allies on the Perseus.