Ok, so I have this head canon where whenever Nico goes off alone into the Underworld it’s not “just to hide away from the living” or be a loaner at all. I mean, the kid KNOWS people down there. Those people never get visitors, never get attention, and Nico knows he can talk to them and be a goof all he wants because none of them will judge him at all for that kind of thing and care more about him visiting them.
Take Charon for example. The guy has (in the books, mind you) confessed to hating his job and not getting paid well enough for the amount of work he does, not to mention having to babysit all the freshly departed souls waiting to be ferried down the River Styx. It’s all work and he kind of shows his fun side in his choice of suits.
I’ve always wondered why Nico told Minos he was “respecting the dead” by bringing them McDonalds as well as camping out along the Styx and then I got the idea that he’s just really comfortable there. Probably made friends with Charon.
lol, I can see Nico getting his training by racing Charon’s boat while on foot along the banks (various monsters, obstacles, shadow-stuff), and if he beats the ferryman to the end, he can get a free ride back up the river or something, since no one is on the boat but Charon on the return journey… and Charon loves McDonalds. So they probably have a lunch break then too.
I also picture him carrying a Greek kopis rather than the western short sword or even the spatha I see him drawn with. Head canon again, mainly because it is a type of blade that’s small but packs a lot of punch with minimum effort.