Not Fighting, But Still Dying

Even after everything Vaan said, Emperor Renardier, Ulrich Salazar, and the other Aura Lords did not appear to be listening to him; they were completely and utterly preoccupied and distracted by the blue flames' presence.

What the actual fuck was going on?! Why wasn't the antimagic field working?! How could the young man still use fire magic?

Even if Emperor Renardier and Ulrich Salazar were both existences that achieved peak Transcendent rank in strength one way or another, they were still, in the end, peak Transcendents, nothing more.

The Demigod rank, which they would refer to as Beyond Transcendent rank, was uncharted territory. They had no idea the extent of power such beings wield nor their abilities.

As such, they did not know that Demigod-rank beings and above could tap into the limitless power of the universal laws, which did not require mana. Thus, they weren't affected by the antimagic field.