Nico di Angelo and Will Solace? Now that's a pairing that honestly took me by surprise when it became canon. I was deep into the Percy Jackson fandom for years, mostly reading Percabeth stuff, and then 'The Blood of Olympus' happened. It felt a bit sudden, you know? Like, we got a few scenes and then bam, they're a couple. That left so much room for exploration, which is exactly what fanfiction stepped in to do.
A huge chunk of the fics out there are what I call 'gap-fillers'. They take that little moment from the infirmary in 'The House of Hades' and stretch it out, imagining all the awkward conversations and tentative steps that must have happened off-page. You'll find a lot of sweet, fluffy one-shots about Will dragging a reluctant Nico into the sunlight, both literally and metaphorically. They're comforting, like a warm blanket.
But the stories that really hooked me are the ones that dive deeper into the aftermath of Tartarus and Nico's history. There's this brilliant AU series that reimagines them meeting in a modern, non-demigod coffee shop, where Nico is a barista with a mysterious past and Will is a med student. It completely strips away the mythological context but keeps their core personalities intact, which is a fascinating study in character. Another one I keep going back to is a longer, angsty piece that deals with Nico's trauma and Will's struggles with being the perpetually sunny healer who might not know how to fix this. It gets messy and real in a way the middle-grade books often couldn't. The search tags you need are 'Solangelo' (their ship name), 'Post-Blood of Olympus', and 'Alternate Universe - Modern Setting'. Sorting by kudos on AO3 usually surfaces the classics.