There's a hint about it in the fiction presenting the human ancestry in the core book. A lecturer is talking about various existential threats in the past that have been vanquished by groups lead by humans, and one of them is "We watched Cthrion Uroniziir try to reduce the timescape into one singular universe, wiping out reality as we know it. She was defeated, and we see her cage every day¹." with a footnote saying "¹ Professor Cilliarwn did not elaborate on this."I'M THE EXISTENTIAL THREAT! RRRRAAAAAAAGH
but seriously that's metal as hell. "The sun contains an eldritch horror that, if released, can singlehandedly end reality" IS a very funny coincidence though.