Sapporo, Japan, 2008. Modern times. A sudden, unexplained wave of destructive events has just begun. Authorities blame it on a shadowy group of thieves, murderers, and maybe even the Yakuza. Four girls know better, though. Blessed by the Animal Lords, they oppose the terrible organization, VEGAS (Vigilant Environmental Group for Area Sciences), which in an attempt to enslave mythological creatures, has created a foul venom, the Titan Poison, that transforms humans into dark monsters, and worse, has made the animal spirits go berserk, transformed into Titans. The four Aces must struggle to re-seal the Animal Lords and combat VEGAS to prevent their world from falling into chaos, while shielding people from the terrible truth to avoid panic; and all this, while continuing their normal, highschool lives.
While the four girls work independently, VEGAS is an extremely well organized and well hidden organization; their public front is that of benefactors, from supplying homes with free power, to providing shelters for the homeless, to rehabilitating criminals for society. Though their real purpose is much more sinister, no one truly knows where VEGAS HQ is located, and none of the public front buildings seem to lead to it, or even have workers who know what's truly going on. VEGAS is very good at covering their trail; and though the city is starting to, slowly, notice something abnormal is going on, most dismiss it.