He's a Mantis from the Mantis Tribe, who grew up knowing that they were not made for fighting. From a young age he avoided violence, choosing more peaceful activities instead. Once he came of age, right before the combat trial that would earn him the title of a warrior (or end in his death, if they were to fail), he vanished without a trace. To the tribe, he was presumed dead. In truth, he escaped with the help of his once childhood friend and now mate, Einarr, and traveled far away towards the surface. He reached Dirtmouth, and decided to settle in there. The town was peaceful, and they knew the other Mantises stayed away from the surface. In their new home, he decided to pursue his old passion: baking. Once he honed his skill, he opened a bakery in the town.
Nils is squeamish and repulsed by violence, particularly the bloody kind. Moreover, while he wants to believe that he's safe in Dirtmouth, in the back of his mind he's still afraid his tribe might try to look for him, and he would rather not imagine what they would do if he found them. He keeps informed of their whereabouts thanks to his secret visits with Einarr, though Nils constantly worries what would happen to his lover if the tribe found out the truth behind his disappearance.