Several weeks before the Allied Forces launched an operation to reclaim the Northern Regions…
After Thirteen had talked to the Centipede King and formed an alliance with it, he also visited another King of the Rigel Continent, which was Death Lord Erasmus.
Through Zed's and Evuvug's story, he had gotten familiar with the Death Lord and thought that there was a possibility to come to a compromise with him.
The teenage boy understood that the Centipede King wasn't the most trustworthy of monsters, given that it readily betrayed Evuvug so that it could raise its ranks.
From the start, he and Jalrog both knew that their alliance was only a way to achieve their goals.
Once these goals had been met, the agreement they had could easily be broken.
Thirteen didn't want to put all of his eggs in one basket, so he reached out to the Death Lord under the cover of darkness.