The latest episode of Dr. Stone Science Future Part 3 delivered a major emotional shift. Episode 4 moved away from just building cool new gadgets and focused on something more personal. The team finally created a computer, but the real story was about Ryuusui Nanami and his older brother Sai.
The episode showed that after 3,700 years, two brothers who grew up in a difficult family finally found a way to connect. It was not about science winning the day. It was about one simple honest moment on a ship that fixed a broken relationship.
Senku Builds the First Computer
The episode opened with Taiju and Ukyo returning to North America. Their mission was simple: revive more people from stone. When they got back, Senku Ishigami dropped some big news. He built a computer.
This was not just another invention. A computer is the foundation for everything needed to go to the moon. In the previous episode, the team revived Sai in India. Everyone thought Sai was just a math genius. But he turned out to be much more valuable. He had memorized entire machine code for Dragon Quest. That meant he could write software from memory. Senku could handle the hardware, but he needed Sai for the digital brain.
When Sai saw a simple computer circuit light up for the first time in thousands of years, it was a powerful moment. No one had seen a working circuit since the petrification. For a man who spent his entire life coding in his head, seeing that light meant everything.
The Group Photo That Hurt Both Brothers
The team built a fax machine to send messages across long distances. Taiju and the others sent back a group photo from America. Everyone gathered around to look at it. Everyone except Ryuusui and Sai.
Gen Asagiri noticed right away. Something was wrong with both brothers. Later that night, Gen went to find Sai. He wanted to understand why a simple photo had made the Nanami brothers so quiet. Chelsea showed up at the same time. She asked Sai directly if seeing old school friends in a photo reminded him of his bad childhood.
That is when the truth came out. The Nanami brothers were left out of family pictures. They were left out of the family entirely, as if they did not belong. Sai was forced to focus only on mathematics, treated like a tool rather than a person. And no one could control Ryuusui. Neither brother fit the image their family wanted to show the world.
For years, Sai thought Ryuusui was using him. Every invitation, every game they played together, Sai saw it as Ryuusui taking advantage of his skills. That misunderstanding sat between them for a very long time.
A Game of Chess and One Honest Sentence
The quietest but most important scene happened when the two brothers played chess. Ryuusui barely said anything during the game. Then he admitted something that seemed completely out of character. He told Sai the ship would be lonely without him.
This was a side of Ryuusui no one had seen before. He is usually confident and focused on his own goals. But in that moment, he showed real vulnerability. He finally told his brother the truth. He did not want another mathematician or another tool. He just wanted someone close who understood what it was like to be excluded.
Gen interpreted Ryuusui’s wish to have a brother not as having another mathematician, or something to use, but just someone who would be close and understand what it was like to be excluded from other people’s company.
The ship was set to leave at dawn. Sai had no plans to be on board. But when morning came, he stood on the deck. The episode ended without a big scientific victory for Sai. Instead, he got something he probably wanted more. A brother who was willing to stay close.
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Release and Streaming Information
Dr. Stone Science Future Part 3 Episode 4 released on April 23, 2026. The episode is available to stream on Crunchyroll for viewers in North America, Central America, South America, Europe, Africa, Oceania, the Middle East, CIS, India, and Southeast Asia.
Fans in selected Asian regions can also watch the episode on Ani-One Asia’s YouTube channel with a membership. The episode is available with English subtitles at the same time it airs in Japan.
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