ONI's is mass produced exoskeletons for bodyguard purpose. These unit build based on Furcas. Altough they dont as powerful as Furcas, ONI's can be used up to 8 hours every 24 hours. Because the ONI's itself doesnt have any particular elements, they imbued with 4 different elements based on their color. The green one often used as a spy, because of their agile trait. Maybe if you collected all of them, in future something good will happen.