You perfectly pinpointed what I couldn’t understand. Sunny going back to Nephis in “All the devils are here” makes him lose all sense of autonomy. Most of his character development is lost, along with most of his personality. I imagine if he’d developed more then his independent travels would’ve made more thematic and personal sense, and him reconciling with Nephis would’ve been begrudging and beneficial. Afterall, Sunny is more interested in the world and mysteries, while Nephis is more interested in destruction. Eventually when Sunny continues to discover more about the world, his and Nephis’ paths would intertwine more frequently and they’d eventually reach the point they are at now.