Dr. Stone › Saison 1 Dr. Stone : Stone World

Chapter 20 — Episode 20

First, the episode opens with Senku presenting his roadmap to build a mobile phone in the Stone World, explaining that the immediate goal is actually a simple horn/communicator rather than a smartphone. Gen expresses skepticism about the plan's feasibility, but Senku confidently declares that science will reach the goal 10 billion percent. The group then discusses their timeline, with Gen impersonating Tsukasa to analyze the enemy's strategy — concluding that Tsukasa will delay his attack until after winter, giving the Kingdom of Science until spring to prepare. Hyoga, shown on Tsukasa's side, notes that Homura is already surveilling Senku's group, and Tsukasa decides to keep Taiju and Yuzuriha under monitored observation rather than harm them. Then, in the middle of the episode, Senku explains the basic science of sound and electricity to an enthusiastic Chrome and Kaseki as the village works together on the phone project. The group makes cotton candy using gold spun into fine wire for coils, and Senku deliberately sends a portion to Homura — the enemy spy watching them — calculating that news of sweet food might tempt some of Tsukasa's followers to defect. Luri quietly observes that beyond strategy, Senku simply wanted to share a treat with a lonely girl. Meanwhile, Chrome secretly disappears with Kaseki for three days straight, working on a mysterious invention. Finally, an exhausted Chrome returns and reveals his creation: a water wheel, independently invented from scratch after being inspired by watching Ginro and Kinro spin the cotton candy machine. Senku is genuinely impressed that Chrome developed it with zero prior knowledge. At the end, Senku declares that with gears and a water wheel now available, the era of human-powered labor is over