While ignoring the struggles of the Heavenly Dao, Kai Syaoran went to work on the serpent.
The first thing he did was remove any limits on the serpent's power.
He wanted it to become as powerful as possible, so he began changing it from its very core, removing all its memories and giving it new ones.
He increased its affinity for chaos to the maximum. By doing this, the serpent gained a new physique that had never before. This was the Chaos God's physique.
Kai Syaoran made its scale impenetrable and its size increased to epic proportions.
The Crimson realm was no longer large enough to hold it. Kai Syaoran had to manipulate space around the serpent for it to fit in the realm.
The serpent saw all this and it could do nothing to stop him.