Hono Mizu was once a port town that thrived financially presumably through fishing and exporting. The entire city sank into what would become the Boiling Sea due to underwater volcanic activity.
Many years later, Kai and Nya then were forced by Krux and Acronix to retrieve the blade in order to save Master Wu from the effects of the time punch. Having no lights, Kai used his power to see. Then, Nya used her power to slide them down to the library. To get to the Time Blade, the first had to get past the Geoatomic Rock Monsters using their Fire and Water combined to shrink the monsters. Finally, they put the Dragon Blade and both hold it to unlock the vault. Kai took the Time Blade, which triggered a booby trap destroying what was left of Hono Mizu.
- Mizu means water, flowing or liquid and Hono comes from Honolulu which means calm port or sheltered harbor, so Hono Mizu presumably means "calm water."