Poseidon (Ancient Weapon)

A 'living' Ancient Weapon: not an object, but a Mermaid Princess able to command the giant Sea Kings.

Poseidon is the title borne by an extremely rare mermaid able to call and command the Sea Kings, creatures capable of sinking whole continents. The current Poseidon is Princess Shirahoshi of Fish-Man Island. In the Void Century, Joy Boy made a pact with the Poseidon of that age and left her the apology Poneglyph in the Sea Forest.