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"No. No. No! Like I've said, I'm no mathematician! I'm a programmer!! [...] All I want... is to code!"

— Sai Nanami, Dr. Stone, Chapter 205

Sai Nanami ( (なな) () SAI (サイ) Nanami Sai) is the son of the owner of Nanami Conglomerate and the older brother of Ryusui Nanami. He is a mathematical prodigy and is said to be "a million times" better than the average person.[4]


Sai is a young man of moderate muscular and scrawnier than most. He has mid-length dark hair that is extremely messy, slightly wavy, and frizzing out at all angles. His hair is mostly pushed towards the right side, away from his left eye. His eyes are almond-shaped, similar to Ryusui's, and has a slightly visible eyelash on the outer corners. His eyebrows are mostly even, with a slight feathering at the top of his arch. His petrification scar covers both his hands and most of his forearms, with a jagged edge near the end.

His outfit consists of a plain white shirt with a stiff popped collar, and short sleeves with the bottoms cuffed. It is laced in the front with ribbon, creating three X's. His pants are a solid black and have a slight flare at the bottoms, held up by a knotted belt with a belt buckle in the shape of a "C" with a "+" in the middle. All the hems are torn-looking rather than cleanly cut. His shoes appear to be of a modern shape with small heels, also solid black.


In contrast to his ambitious and self-assured younger brother, Sai is a more timid and self-conscious person who doesn't think much of himself. He brushes off his talent for quick mental math as nothing special, and shied away from the attention and pressure it brought him. He has great a passion for video games and coding, and fled to university in India instead of following actuary duties for his family's company.[5]

He is an intelligent young man who more than excels in his academic pursuits. He is a habitual person as his brother correctly speculated that he would have been alone on his laptop in a place with a decent signal prior to class.[6] He has issues with his family, or at least Ryusui, as the mere sight of him caused him to run.[7] Sai's disdain for his family stems from them trying to exploit his talents for their own ends, but he seems to appreciate when people treat him like an average person rather than a prodigy.[8] The elder Nanami is prone to panicking and dismay when faced with unpleasant or overwhelming situations, like reuniting with his brother, running Nanami Corp., or living in a world without a computer.[9][10] That said, he is still capable of resolving himself and moving forward towards what he wants, writing coding that, at the time, didn't have much use simply to preserve his favorite game should the technology become available.[11]

Abilities and Skills[]

  • Mathematics: Sai is a prodigy in mathematics, being able to easily solve incredibly complicated questions in his head in seconds.[12] Sai's level of mental maths is slightly slower than using a calculator.[13][14] Ryusui often employed his skills to help create simulations for his whimsy.[15][16]
  • Memorization: In conjunction with his mathematics abilities, Sai had a brilliant memory, something that would likely be required in order to solve the things he does. Sai was able to recall and write down the entire coding script for Dragon Quest, a code so long it filled up all the walls in his cabin.
  • Coding: Though known to be a prodigy in mathematics, Sai's passion lies in coding, and he claims himself to be a programmer rather than a mathematician.[10] Sai can easily reproduce the code for famous games such as Pac-man or Tetris despite the low-level programming necessary.[17] He can also code more useful things for the Kingdom of Science quickly such as the voting program and the rocket simulation.[18] Finally, Sai would never taint his coding to achieve results he wants, much like Senku who would never lie about science to anyone.[19]
  • Teaching: When in India, Sai taught math at the university. He applies his teaching skills later with Suika and Chrome when they ask for his help making the rocket.[20]
  • Ambidexterity: Sai is shown not only to be capable of writing with either hand, but doing so simultaneously.[21]



Sai and Ryusui were not born into the matriarch of the family, and as kids were often left out of family photos.[22] As a child, Sai was an incredible mathematician. He could do large multiplication questions in his head, and sometimes even did harder questions than he was supposed to, such as mistaking a plus sign for a multiplication sign. His teacher was left in awe and alerted Sai's uncle that he is a "bona-fide prodigy". From a young age, the Nanami Corp. forced Sai to study rigorously solely on math, getting a grasp on linear algebra, topology, and set theory quite easily. Nanami Corp. wanted Sai to be the company's dedicated actuary. However, Sai did not want this and fled to India.[10]

Rather, his passion lied in gaming and coding. Sai would often sneak away to play games, and even programmed some himself. However, his skills were desired by his younger brother Ryusui, who told Sai to polish all his skills, which the timid Sai did not believe he could do. Ryusui wanted Sai's skills to help him in endeavors, such as building model ships or race courses. Sai would run the numbers of the models Ryusui made, and even designed programs for him, such as sailing simulators.

One day though, Sai had enough, and flew out to India to studio at a university, where he would remain until the petrification.[10]

Globetrotting Arc[]

En-route to India, Ryusui mentions that he wants to revive someone named Sai for their brilliant math skills. They soon find and revive Sai, who is a little confused by the situation but thanks them profusely. Until he spots Ryusui, and begins screaming and running. He is quickly caught by Kohaku, and protests that he doesn't want to return to Nanami Corp, at least not while Ryusui is around. He then reveals that Ryusui is his little brother, surprising everyone.[23]

While Ryusui told everyone about how much of a genius Sai was, he denied it, saying it was Ryusui making the same wild claims he made when he was a kid. Chelsea told Sai she was happy to have him as a regular friend, much to Sai's delight. When Ryusui told everyone of Sai's skills, he clapped his hands in frustration claiming mental maths is pointless, and everyone in the world could do it given enough time. Ryusui told Sai he desired his mathematical skills above all else, but Sai ejaculated that all he wants to do is code. Sai asked how long it would take for them to build a proper modern computer, and Senku replied 5-10 years. Sai broke down, asking why they even revived him if he can't do what he feels he was meant for. Sai locked himself in his cabin sulking, not even collecting his meal from Francois. After some thought, Sai decides he doesn't want to sit around and waste away, so he begins writing the code for Dragon Quest on his walls in machine code. When the others see what he wrote, Senku decides they'll make a computer after all.[24]

Sai asks Senku on how they would even make a computer in the Stone World, and Senku explains they'll use parametrons rather than semiconductors. To demonstrate their use, Senku builds a half-adder circuit for Sai to test, which fills him with relief. By adding more circuits, they'll eventually get the computer Sai wants, which gives him hope.[25]

When the Perseus prepares to move on to their next location, Sai bids them farewell as he planned to stay in India to work on circuit diagrams. Ryusui tells him he's coming with them, which Sai adamantly refuses. He was certain Ryusui had not changed. Sai later sees the group photo sent from Corn City, and thought back to his and Ryusui's childhood. While in his room alone, Chelsea bursts in, asking what his deal is with group pictures. Sai explains his childhood to Chelsea and Gen, who followed her in with tea. By the end, Chelsea is in tears and Gen explains that Ryusui simply wanted a brother, and was never forcing him to do anything. After some more time alone, Ryusui comes in asking to play a game of chess, which Sai began to deny before ceding. After some bonding together, Sai decides to join the Kingdom of Science on their journey, and reforging his relationship with his brother.[26]

Once the calculator was complete, to test its power, Gen decides to host a math contest. The four contestants are: Chrome, Senku, Sai, and Magma using the calculator. Gen presented them with a rather complicated question, which Magma, using the calculator for the first time, answered correctly. Sai and Senku quickly confirm the answer is correct.[27]

After finding out the mission to the moon will be a one-way trip, Chrome and Suika, the two rookie scientists, request Sai's help in building the return rocket. Sai tells them it won't be easy, but they know already and are ready for the challenge. Sai begins giving them lessons.[28]

Moon Mission Arc[]

When Ryusui later expresses desire to bring back entertainment, Sai agrees, acknowledging how hard life is without enjoyable things, thinking back to his games. Sai is on the verge of tears when the finished computer is finally brought to him, and he states it is on par with the Nintendo Entertainment System. Sai produces programs in seconds, and everyone begins playing classic arcade games on the new computer. Sai and Ryusui spend the night playing a virtual chess game, and are proud of how far they have come with science.[29]

After years of work and training, Suika and Chrome presented their return rocket plan to Sai, which he was happy with, and allowed it to be shown to two professional scientists, Senku and Xeno. Sai had ran the math for the launches, and even Senku said it worked on paper, it just wasn't realistic. In order to decide, a vote was called for which Sai created a voting machine for. Ryusui assured Senku the vote would be fair, as he said Sai would never taint his coding with deceit just as Senku doesn't lie about science. Sai announced the results, and the winner was the two-way rocket plan. In order to achieve a proper two-way rocket, Senku announced they would make the internet, which blew Sai's clothes clean off.[30]

After the internet had been finished and the online meeting occurred, Senku claimed the designs for the rocket would be done online, which Sai claimed was not possible with the primitive computers they were using, but as usual Senku proved him wrong.[31] In order to prepare for the moon mission, Sai designed several programs to help prepare, such maze-making programs[32] or space flight simulators (with gaming bonus rounds).[18]

Sai later helped to program the touchscreen phones system, such as games or emails, though the smaller, more familiar phone sized screen was still connected to a large computer.[33]


Ryusui Nanami[]

He is shown to have trauma with his younger brother, particularly in regards to Ryusui's pushy and ambitious nature clashing with his more timid and self-conscious personality, causing him to escape to India before the Petrification. He believed that Ryusui wished to use his skills, but after Gen pointed out that Ryusui probably just wished to spend time with him, there is a sense of reconciliation between the brothers.

Chapter Appearances[]

Chapter Appearances
Globetrotting Arc
201. Morse Talk Absent
202. Ryusui Corp. Absent
203. Missile Heart Absent
204. The Universe is Written in the Language of Mathematics Debut
205. Universe of Zeroes and Ones Appears
206. Dawn of the Computer Appears
207. Linking the Circuit Diagram Appears
208. Science Transcends Humanity Appears
209. The Rocket's Hard Truth Appears
210. Not One-Way Appears
211. World Tour for Resources Pictured
212. Final Part: Stone to Space Absent
Moon Mission Arc
213. Unknown Known Appears
214. Stone World's Earth Defense Force Appears
215. Long, Long Road Appears
216. Hello, World Pictured
217. Science Underdogs Appears
218. WWW (World Wide Workshop) Appears
219. Three Heroes Pictured
220. A Desire for All Appears
221. Entrusting It All Pictured
222. Science Road Appears
223. 0 Absent
224. In Space Absent
225. Docking Appears
226. Giant Step Appears
227. It Was You Absent
228. Life Stone Absent
229. Why-Man Absent
230. Human Absent
231. A Future To Get Excited About Absent
232. Final Chapter: Dr. STONE Pictured


  • Sai was first shown in a pose similar to the Hindu deity Durga. His later multi-armed poses were inspired by Hindu art.
    • Boichi had also wanted to draw cracks on his forehead similar to Sheba's eyes.[34]
  • Since he is of Indian descent and Ryusui isn't, they are half-siblings.
  • Sai's design was Inagaki Sensei's idea, and was based off the Bollywood star Vidyut Jamwal.[35]


  1. 1.0 1.1 1.2 Dr. Stone: Kingdom of Science Encyclopedia, Page 144
  2. Dr. Stone Manga: Volume 24 — Worker File
  3. Dr. Stone Manga: Chapter 204, Page 13
  4. Dr. Stone Manga: Chapter 204, Page 7
  5. Dr. Stone Manga: Chapter 205, Pages 4-6
  6. Dr. Stone Manga: Chapter 204, Page 11
  7. Dr. Stone Manga: Chapter 204, Page 15
  8. Dr. Stone Manga: Chapter 205, Page 2
  9. Dr. Stone Manga: Chapter 204, Page 16
  10. 10.0 10.1 10.2 10.3 Dr. Stone Manga: Chapter 205, Page 6
  11. Dr. Stone Manga: Chapter 205, Page 13
  12. Dr. Stone Manga: Chapter 205, Pages 2-3
  13. Dr. Stone Manga: Chapter 205, Page 3
  14. Dr. Stone Manga: Chapter 208, Page 14
  15. Dr. Stone Manga: Chapter 207, Page 11
  16. Dr. Stone Manga: Chapter 220, Pages 3-4
  17. Dr. Stone Manga: Chapter 213, Pages 11-12
  18. 18.0 18.1 Dr. Stone Manga: Chapter 220, Page 4
  19. Dr. Stone Manga: Chapter 217, Page 12
  20. Dr. Stone Manga: Chapter 210, Page 14
  21. Dr. Stone Manga: Chapter 205, Pages 11-12
  22. Dr. Stone Manga: Chapter 207, Page 10
  23. Dr. Stone Manga: Chapter 204, Page 19
  24. Dr. Stone Manga: Chapter 205, Page 19
  25. Dr. Stone Manga: Chapter 206, Page 17
  26. Dr. Stone Manga: Chapter 207, Page 20
  27. Dr. Stone Manga: Chapter 208, Page 15
  28. Dr. Stone Manga: Chapter 210, Page 19
  29. Dr. Stone Manga: Chapter 213, Page 12
  30. Dr. Stone Manga: Chapter 217, Page 19
  31. Dr. Stone Manga: Chapter 218, Page 14
  32. Dr. Stone Manga: Chapter 219, Page 10
  33. Dr. Stone Manga: Chapter 222, Page 14
  34. https://www.youtube.com/watch?v=EZQLCsjJDsI [Boichi, PLZ draw this!] Sai and Ryusui Brother and kid and youth Suika
  35. https://www.youtube.com/watch?v=EZQLCsjJDsI [Boichi, PLZ draw this!] Sai and Ryusui Brother and kid and youth Suika

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