It's the key you use to get into the Tonberry Hate Reset room at (F-11) of the first map of Temple of Uggalepih.
You get it from the quest as listed by trading three Gold Beastcoins to Magephaud in (I-8) of Norg. This is nasty in some servers. On Phoenix for example, they're 25k each in the cheapest AH (and 35k at Norg, of course).