Recruiting the 4 directions

The Guardians of the Directions are four ancient monsters of incredible power who each represent one of the four cardinal directions. They are: Kraken (south), Sphinx (west), Yamata no Orochi (east) and Poseidoness (north). Each of them requires a special event to be recruited.

Kraken
The Queen of the South Seas and the first of the Guardians you encounter.
 * 1) Complete the South Sea Temple quest to get Kraken in your inventory (as Dried Squid).
 * 2) Go to the North Sea Temple and talk to and defeat Poseidoness. She will then direct you to Queen Mermaid.
 * 3) Talk to Queen Mermaid to restore Kraken's true form, and the latter will join you.

Sphinx
The second Guardian encountered. As of Part 2, Sphinx is the only companion with access to the Advanced Race "Sphinx".
 * 1) Progress the game until the quest for the Orbs.
 * 2) Talk to Sphinx and defeat her (this can be done before or after getting the Yellow Orb from her). Sphinx will join the party.

Yamata no Orochi
The third Guardian encountered. She is arguably the easiest of them to recruit, as she simply requires you to defeat her.

Poseidoness
The Queen of the Northern Sea and the last of the Guardians you encounter. Her recruitment is tied to that of Kraken.
 * 1) Recruit Kraken (see her entry above).
 * 2) Talk to Poseidoness with Kraken in the party to recruit her.