Ragnarok's tails couldn't do anything to it before but that is changing now that the defense of its scales is reducing constantly. The devouring is also reducing its strength so its chances of escaping are reducing by the moment.
Unfortunately for it, the darkness is devouring any type of creation it uses its concept to create so it couldn't bombard Ragnarok the way it did with Rinoz. It decided then that it must not remain within Ragnarok's embrace any longer. So it summoned its domain when all else didn't work. Ragnarok did too.
He felt the law matrix become agitated immediately after the domain of the fountain of life was deployed. He couldn't allow himself to fall under the domain of a dragon. He might not be able to break out of it once it happens. After all, the dragon is the real deal with an inner world right here whereas he is just borrowing the domain of a world beast. So he nipped any future problems in the bud by evoking his domain.
