Mavuika was the Pyro Archon when her first life ended, so the answer is Mavuika herself.

In Natlan’s lore, she is described as the latest Pyro Archon, and the sources I found identify her as the Pyro Archon of Natlan.

If you meant the archon of a different nation at that moment in the story, tell me which quest or scene you’re referring to.