Fish-Man Island Air-Regulating Cannon

Structural lore — the island’s stored “air tank,” dischargeable through a cannon to shape a controlled breathable bubble.

What we know

• Ch. 641 pp. 15–16 — Fish-Man Island maintains a stored reserve of air (an “air tank”) that can be discharged through an air-regulating cannon to shape a controlled bubble. Introduced on-page as the defenders’ plan to fire the tank’s entire reserve into a single giant bubble “that can completely envelop Noah,” giving Luffy breathable air to fight on the deck of the falling ark.
• Ch. 641 pp. 15–16 — Explicit limit: the bubble has no buoyancy of its own, so “the air can’t actually lift Noah” — it cannot stop the ark from sinking; it only buys Luffy air to fight.
• Ch. 641 pp. 14–16 — Operated by the island’s defenders / Neptune Army; the plan is coordinated to Luffy by Fukaboshi via a baby Den Den Mushi.

Chronology / structure

A piece of Fish-Man Island civic infrastructure introduced at the arc’s climax: the island regulates its own air supply (it sits ~30,000 ft underwater, lit by the Sun Tree Eve), and that same air-management system can be weaponized defensively as a single deployable bubble.

Open questions about this topic

Cross-links

• Location: Fish-Man Island
• Operators: Neptune Army / the island’s defenders
• The threat it answers: Noah (the falling ark)
• Coordinated via: Den Den Mushi