Pure White Shell (純白の貝殻 Junpaku no Kaigara) is the fourth chapter of the Dr. Stone manga.
Senku adds that Tsukasa is too strong. Taiju, while still amazed at Tsukasa's strength, asks him what's so bad about it. Senku argues that Tsukasa may be a bad person and unstoppable in the non-weapon world.
In the tree house Tsukasa introduces himself properly and Senku explains the situation to him. While cooking, Senku starts a quiz: "What's the most important thing that we need in modern civilization? 10 billion points for the right answer." Tsukasa and Taiju guess, but they don't come up with the desired answer. The answer is calcium carbonate. "Big guy, this is the shell that was so useful in taking care of your beard. By just crushing it to dust, we can create something - carbonate!" He goes on to explain that there are four deadly important ways to use it: "First! Agriculture. We can get rid of hydrogen ions with calcium carbonate. In other words, it levels up the soil. Second, by heating it and mixing it to sand, we can make mortar. It's like baby cement. We could build a big oven or a house with it. Third! Soap. In this world where disease means game over, this small block that eliminates bacteria is the life stone that replaces doctors. It's Dr. Stone!" Tsukasa is shocked by Senku's wealth of knowledge. He compliments him, to why Senku shows skepticism towards him. This skepticism is compounded with Tsukasa's statement: "You could end up recreating modern civilization from scratch. Yeah ... I just thought that." Taiju recalls that Senku has left out the fourth path. But Senku insists that there are only three.
As they gather seashells by the sea, Tsukasa talks: This Stone World, it's free. To begin with, shells don't belong to someone. Even the sea or the land. Long ago, there was a poor little boy. He tried to make a shell necklace. For his sister who was going to undergo surgery ... She loved the little mermaid. And then appeared a guy just like this", he leans toward a petrified man, "A middle-aged man who had the fishing permit in the area, with his alcohol tainted breath. The boy who was gathering shells ... was in fact stealing them, or so said the middle-aged man. The boy was hit until his face changed. He couldn't make his sister into a mermaid until the very end ...", and crashes the statue in pieces. Senku alerts him that he has just killed a human being. Tsukasa rings out to him that he fully understands it and proposes to revive only young people to build a new structure of society in which nature or or other belongs to no one. Senku rejects on the ground that "he's a technology loving kid, who's excited by mecha, space and doraemon." They stare at each other for a while and Senku regrets his revival. He considers to keep the miracle water secret. But his plans are dying. Taiju runs screaming with enough miracle water for Yuzuriha towards them.