Weapons of Science (科学の武器 Kagaku no Buki) is the third episode of the Dr. Stone anime.
After reviving Yuzuriha, Senku and Taiju are confronted by Tsukasa, now dedicated to "purifying" the Stone World of adults. Senku and Taiju attempt to fight back and convince Tsukasa to forgo his plan, but he refuses.
Senku, Taiju, and Yuzuriha journey to Hakone in order to create gunpowder capable of harming Tsukasa. However, Tsukasa discovers the plan, and is in pursuit to stop them.
Although Senku refuses Tsukasa's offer to purify humanity, he still knows the strongest highschooler is too much of a threat. He hopes Tsukasa will stay under control until he learns about the revival fluid. Taiju abruptly arrives on the beach and reveals the batch of miracle fluid for Yuzuriha is ready, stunning Senku with his horrible timing. Tsukasa asks about the liquid and Senku tells him he'll get an explanation back at camp.
Back near the Camphor Tree, Senku reveals they're just short of enough liquid. Taiju volunteers to go get more but Tsukasa decides its better if he goes instead. Senku used this as a diversion to get Tsukasa away, even at the cost of revealing the location of the cave. He acts quickly to formulate the proper liquid, confusing Taiju. Senku explains he doesn't have an interest in Tsukasa's pure world and Taiju understands that something happened between them. Tsukasa isn't just a good guy, he's a murderer.
Senku makes Taiju pour the liquid on his crush's stone body. He explains the liquid takes time to react, but when it does, it creates a cascading effect that release Yuzuriha's entire body from the stone. They have a heartfelt reunion but Senku interrupts because the couple must choose between either running away somewhere far or staying to fight back against Tsukasa.
Tsukasa suddenly returns and claims he's culling the tainted adults and not murdering them. In reality, he's not even hiding his murderous intent from Taiju and Yuzuriha. Taiju decides he must stop the strongest highschooler here and now. He charges for him, forcing Senku to back him up with a crossbow he developed in secret.
Tsukasa snatches the arrow out of the air and delivers a powerful knee to Taiju's head. Somehow, Taiju is the first person to remain on his feet after taking one of Tsukasa's hits. Taiju claims he doesn't hit people and offers to let Tsukasa hit him in exchange for sparing humanity. Tsukasa doesn't understand the bargain and the fight comes to an abrupt end when Taiju suddenly passes out.
Senku decides they must pretend to run away while searching far and wide for weapons of science to fight back against the strongest human currently alive. They must develop weapons before Tsukasa finds them or its game over. They travel for over six hours but get slightly lost while searching for there girl. Without proper GPS or landmarks, it seems improbable to find the current path. However, Yuzuriha recognizes the Great Budda Statue that remained since it was built from bronze.
They take the night to rest and continue traveling in the morning. Meanwhile, Tsukasa becomes aware of the stakes after seeing through Senku's ruse. Senku and the group eventually reach hot springs and he reveals that they're going to make gunpowder to fight back against Tsukasa.
Anime to Manga Differences
- In the manga, Senku obtains the black powder during the hot bath while he obtains it right away after reaching the mountain peak in the anime.