Chapter 604

Chapter 604 is titled "Into the Depths".

Short Summary
As the Straw Hats venture deeper into the ocean Nami, with some help from Franky and Brook explains how different parts of the underwater current system work. Caribou﻿ and his crew try to attack the ship, but due to Mohmoo, becomes the only one of his crew to make it onto the ship. He pleads for his life and the crew ties him up. The chapter ends with the crew confronting a kraken, and Luffy planning to tame the massive creature.

Chapter Notes

 * Mohmoo reappears. He seems to have been captured by the Caribou pirates sometime after the Arlong arc.
 * Usopp accused someone else of lying for the first time.
 * Even after two years, Luffy is still unaware Whitebeard had died. This is proven after a whale swam by which Luffy thought was the Moby Dick.
 * Deep sea currents are explained.
 * Sanji has to have a blood transfusion due to his continued nosebleeds.
 * A method of rehabilitation is suggested to help with Sanji's severe nosebleeds.
 * Chopper ruins Brook's attempt at a skull joke, leaving the latter momentarily depressed.
 * Sanji kicks Caribou in the face even though he is a Logia user, implying that Caribou either has not trained his Devil Fruit power to activate reflexively or that he decided to take the kick to hide his ability from the Straw Hats.