exploring Percy's canon interactions with Nico from botl and onwards on the level that I am for my fic is making me have a whole new perspective on percico and their relationship...
like Percy. oh, Percy cares for Nico so much and it's subtle at times but he's constantly reaching out at him, checking he's okay, making sure he's safe, inviting him to sit with him, asking him to keep in contact.
yet each time he does, Nico shuts it down with his own logic or brushes him off. there's nearly always something else he needs to do instead of going with what Percy suggests, and Percy always respects that.
at the end of botl, Percy respects Nico's need to leave camp, even if he does try and suggest options on how Nico could be welcome there, and then let's him go without any bitterness or other negativity (he even lightens the mood and makes Nico remember he's still a kid under there).
Percy accepts Nico for who he is and lets Nico go at his own pace. He doesn't push him or drag Nico's feelings down or blame anything on Nico's own actions.
also, at the end of the sword of Hades, Percy respects and understands Nico's need to stay in the Underworld while still offering out his support (by letting Nico know he's there if he needs anything).
Percy understands Nico's need to find out information about his family, get closer to Hades, stay in the Underworld & be one with it.
then, to top it all off, Percy uses his reward from the Gods to make sure Nico has a home, a safe place to go back to, somewhere where he can be accepted.
Nico is part of Percy's loyalty and honestly, I feel like if the two of them had simply got a chance to talk then Nico would have realised just how much he does mean to Percy.