SPOILER WARNING: Details about a quest, mission or other Final Fantasy XI in-game storyline follow.
In ancient times, the Zilart were a race of people endowed with the gift of telepathy (or "whisper of the soul"). There came a time when some of the Zilart lost that ability after being contaminated by the Emptiness; those people were called the Kuluu. The Zilart cast the Kuluu out of Al'Taieu, considering them to be abominations, having been tainted by the darkness. Separated from the cities of the Zilart, the Kuluu settled in Elshimo Island, Fauregandi, and Sarutabaruta, establishing the civilizations that would, in the modern era, be called Pso'Xja, the Temple of Uggalepih, and the Horutoto Ruins.
The Zilart came to fear the rise of the Kuluu, and set out to subjugate them. Amulets were created to allow the Kuluu to communicate with the whisper of the soul. The Dawn Maiden Yve'noile constructed the Chamber of Eventide in the Grand Palace of Hu'Xzoi in order to purge the Emptiness from the Kuluu and allow them to be reborn as Zilart. This accumulation of Emptiness in the chamber unintentionally exceeded the Keeper of the Apocalypse, so Selh'teus sealed it within himself to prevent Promathia from being resurrected.
The Zilart attempted to construct the gateway to Paradise - Tu'Lia. This was opposed by the Kuluu and the Dawn Maidens, as this would mean the end of Vana'diel. Eventually, the Kuluu managed to overthrow the Zilart by sabotaging the attempt to open the gate. In the aftermath of the ensuing disaster, most of the Kuluu were transformed into Tonberries. The few Kuluu who escaped the Tonberry curse attempt to prevent the destruction of the world at the hands of Bahamut, according to the deal struck by Selh'teus.