Let's address the elephant in the room: Pjo!Nico, SoN + MoA!Nico, HoH+BoO!Nico and ToA!Nico are essentially four different characters with the same name.
First off, Nico's character was centered primarily around platonic + familial love, identity in vastly different tempo-cultural environment from the one in which he was born, grief, abandonment and finding acceptance among others. A principle highlight of his character development was coming to terms with Bianca's death:
(Battle of the Labyrinth; in this pivotal scene Nico accepts Bianca must stay where she is: receipt 1)
However, moving on to Son of Neptune, we come across the first major (and highly unfavorable) aberration his character undergoes:
(Son of Neptune, receipt 2)
This was a major disservice to his character development. The Doylist explanation? He needed to be used as a plot device for Hazel's resurrection - which is bluntly put - unnecessary; the doors of death were open, she could've returned simply as an escaped soul.
Now in House of Hades, we run into yet another bad retcon - the crush on Percy and the botched recontextualization. Overlaying a deeply platonic relationship with a major one-sided crush requires a lot of craft, thought and subtlety - work Riordan failed to put in. We can clearly see how Nico's thoughts, attitude and behaviour towards Percy are very different after the retcon; this can be illustrated very easily through by drawing a comparison:
(House of Hades; Nico is implied to be deeply bitter towards Percy: receipt 3)
(House of Hades; Percy tries to thank Nico with regards to Bob the Titan and his experience in Tartarus, only for Nico to snub him: receipt 4)
Vs
(Son of Neptune; like an "incantation": receipt 5)
(Son of Neptune: receipt 6)
(Mark of Athena; Nico and Percy's conversation: receipt 7)
In receipts (3 and 4) Nico is bitter towards Percy alongside the crush, demonstrated by the way he snubbed him.
Now this really does not track at all. Note the tone and choice of words in the receipts 5 and 6- Nico describes Percy as trustworthy, a threat only to his enemies. The word "incantation" - what sentiments does this highlight? Fascination, admiration, a certain degree of reverence even. Do you see hostility or bitterness anywhere?
Note the contrast against how he addresses him in receipt 7 as opposed to the unwarranted snub - he apologizes and explains his situation. In fact, he's in a far worse mental and physical state in Mark of Athena than in the House of Hades.
Another major ham-fisted retcon is the whole "you pushed everyone away" being attributed to his internalised homophobia, instead of being attributed the horrifying trauma which would've made a lot more sense in terms of continuity because if the former were true, Nico would've pushed everyone since Son of Neptune, but we can see there isn't any good truth to the idea:
(Son of Neptune; Frank calls Nico, a gesture Nico reciprocates with a smile receipt 8).
(Son of Neptune: receipt 9)
(Son of Neptune: receipt 10)
We can infer from receipts 8 to 10 that Nico actually tries quite well to interact with people in a environment that was decidedly averse to his parentage.
It's actually simple. Riordan pulled a lot of post hoc changes to fit in the whole crush on Percy +internalized homophobia retcon, which damaged Nico's character significantly.
In ToA, most of his character is flattened to "Will Solace's emo bickering boyfriend", and he barely brings up his platonic relationships with Reyna and Hazel, which were very important to him throughout BoO.
I really like to get to write and read how nico is portrayed in fics because itâs like spinning a wheel of âwhich one of his 100000 canon characterizations of him will he be on todayâ
