If you think about it, their whole dynamic is built on this intrinsic contrast that just begs for exploration. Nico's got that whole brooding, shadows-and-death vibe, which isn't just an aesthetic; it's trauma, isolation, and centuries of baggage he carries in a teenage body. Will is literally sunshine personified, but reducing him to just that misses the point. His healing isn't passive. It's stubborn.
In fanfiction, I've seen writers use this to create a push-pull that's less about fixing each other and more about challenging each other's defaults. Nico's cynicism forces Will to acknowledge that not everything can be fixed with a bandage and a kind word, grounding his optimism in reality. Conversely, Will's relentless, almost annoying insistence on care forces Nico to confront his self-destructive habits.
That tension is where the best stories live. It's not one sunshine boy melting the ice king. It's a stubborn healer learning that some wounds require sitting with the dark, and a son of Hades learning that accepting care is a form of strength, not weakness. Their complementary natures create a balance—Will brings Nico into the light of the living world, Nico helps Will understand the weight and necessity of the dark.