The guardian of the Immortal Sun was Azor, a sphinx connected to Ravnica’s law and to Ugin’s ancient attempt to trap Nicol Bolas. Azor had spent his spark creating the artifact, expecting Bolas to be drawn to Ixalan and held where Ugin could confront him. Bolas never entered the trap.
Azor treated Vraska as a criminal category rather than a person and assumed authority followed naturally from his design. Jace recognised the pattern of a sphinx defining order for everyone around him. As the Living Guildpact, he used the office Azor had helped create to bar him from returning to Ravnica and restrict his interference.
The encounter revealed another failed anti-Bolas plan built on secrecy and certainty. The Immortal Sun was powerful enough to imprison planeswalkers, but its makers had not controlled who would eventually claim it. Sacrifice created a tool; it did not guarantee the wisdom of its use.