Military action
Simultaneously with the crowning of the new Impirator of Laran, a series of betrayals within Achronis' military and government, coinciding with cult uprisings, allowed Laran to retake near all the territory they had lost since the Battle of Kaseibeiut.
The moment that Laran's Impirator claimed their crown, a series of underground Lati cults (Meta: Actual cults, like Lovecraft & demon worshippers, the like) sprung up in many of the most populace Achroni worlds. Specifically, those which Achronis had claimed from Laran during the Mojn Oqinshus push. This allowed the Empire to reclaim many of their lost worlds, ones which had been lost over a thousand years ago.
Most scholars believe that the timing of these revolts was no coincidence. The remnants of information about the Impirator and The Devoted suggest they were extremely patient and very good manipulators. That and the fact that most of these uprisings occurred on planets with Lati ruins that had yet to be purified by Nameless, suggests some ritual or leaking Inkallu corrupted the populace of said planets, allowing them to fall under the sway of the Impirator. This could give credit to why he faced little challenge to his position besides the standard competition. A series of quick victories and successes would have granted him the presitge to stay on the throne long enough to consolidate security.
It will likely be unknown forever, as much of the information about Laran in the century before and half a century after the Impirator's ascension has been purposely erased by The Devoted.