Senku, Chrome, and Magma embark on a dangerous cave expedition to find rare minerals. Despite their differences and rivalries, they must learn to work together as a team to overcome natural challenges and retrieve the valuable mineral crucial for rebuilding civilization.

The tension between scientific progress and raw power is highlighted through the conflict between Senku's logic-based approach and Tsukasa's reliance on strength and intimidation. The creation of a working telephone becomes a symbol of Senku's vision for an advanced society.

The invention of the telephone represents more than technological advancement; it's a milestone in restoring human connection. The ability to communicate across distances becomes crucial for exchanging information and strengthening alliances in Senku's plan to unite humanity against Tsukasa.