After Vaan's fleshly body was completely broken down, the bloody mass mixed with the cluster of aura and life and gradually fused in the center of the cosmic flow.
In the process of breaking down his body, the invisible shackles of Chaos's heavenly laws were also snapped off, allowing it to become something that they couldn't control and restrict.
It was unknown when such shackles of the heavenly laws had attached themselves to his body.
It might have happened when he had entered Chaos for the first time.
No, it might have already existed since the day he was born. After all, Pangea and Gehenna were already connected at that time and the invisible tendrils of Chaos's heavenly laws were reeling in Pangea's chaosverse.
After the invisible shackles of the heavenly laws broke, they tried to reform and reattach themselves to the remains of Vaan's body.
However, his Nihility Law warded them off.