Swarm and Azure are survivors of a race wiped out by the Timelords. They are the race that birthed the Timeless Child and can regenerate. However their regenerative abilities need to be fueled by destroying living things. The same is true for the Timelord ability, only we never knew. The fuel that the Timelords used was the destruction of their civilization. Now Swarm and Azure want to rip apart time and space as revenge. Hence the Flux.