Contingency Plan.

Their plans come down to two objectives. They want to seal him at all costs or allow one of the Supreme Beasts without Supreme Laws to touch him. They have special arrays to accomplish the first option and they have come prepared for the second option too. 

Those Supreme Beasts without Supreme Laws are incapable of making Supreme Laws. They have a concept that can shift into any other concept, and they do this by stealing the concepts of others by touch.

They are the Supreme Beasts who took the path of further awakening and are stuck. But they are very useful. The Supreme Alliance can use them to steal Legion-8's abilities. All they have to do is touch him. This theft is also permanent, so if they succeed, they will have something important to bargain with Legion. 

Legion-8 admitted, "It is a foolproof plan."