First, let me get one thing straight. His name is Nico di Angelo. Not DiAngelo. Not Niko di angelo. It's Nico di Angelo.

Now that I've gotten that out of the way, it's time for the rest of the chapter. Nico di Angelo is a very complex character that not many fanfics can portray accurately. You did not write him, Rick Riordan did. That means there are several things you do not know about him that you will have to answer as best you can. Try your best, and you'll see that it gets easier and easier as you go along.

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Most of Nico's past is unknown, and that means he may have hidden skills. When you add skills, add them for a reason. There are questions you need to ask yourself before you write him and his skills.

These questions are not limited too:

are his special skills?

can he practice these skills?

did he have time to learn them?

does he have these skills?/ these skills contribute to the plot?

these skills/interests/hobbies canon?

The last one is something that you should always ask. This is because people tend to make Nico overpowered, and have random skills that do not make sense. What you add needs to make sense.

Let's say I want to stray away from the canon, and make Nico very good at hand to hand combat. You need to answer where he learnt the skills, when he had time to practice, and if the skills are canon.

Remember, Nico is still only a fourteen year old who is chronically described as scrawny and pale. He knows how to fight, but he's not a master of Aikido, Tae Kwon Do, and Karate. It takes time to learn these skills, and Nico has been away from camp for a very long time.

If I remember correctly, he was a drifter, and didn't spend much time at either camp. It is likely that he doesn't have much formal training, besides the small camp training he received before running away, and King Minos's.

Therefore, he still has a long way before he can fully show all of his skills and battle prowess.

A lot of people want to make Nico some punk rock dude who listens to heavy metal. May I remind you that Nico was born in Italy, very far away from much western influence. Not to mention there wasn't any Green Day or My Chemical Romance back then. The likelihood of him hearing that kind of music is very low, considering he can't use technology. It all comes back to those questions. If it doesn't contribute to the plot, you might want to think twice before including it.

In my opinion, Nico di Angelo is the best character for crossovers. Specifically, pre Giant-War, post Titan-War Nico. You might disagree, but let me put it this way:

Percy has too many attachments, so people end up killing off his family, and the rest of the seven. Annabeth is also too attached to Perc. Leo is a good choice, but he's still on the grid, with social services probably after him. Piper has a rich dad who would instantly call the cops if she was missing. Jason is off the grid, but would probably stay back to help the campers. Frank has praetor duties, and Frank would notice if Hazel was gone. Thalia is with the hunters.

This leaves Nico. They probably wouldn't go looking for him, because he often leaves camp for long periods of time. He's very interesting, so he won't bore your readers. And come on, Nico as a superhero is pretty cool.

A lot of fanfics like to give Nico some crazy trigger that makes him bust down crying, or some other random thing. Don't do that. No matter how enticing that might be, DO NOT DO IT. It doesn't make sense, it's not canon, and frankly, we've heard it a million times before.

Anyways, people make Nico depressed, and often don't portray it right. They want Nico to be some overpowered character who has these crazy weaknesses, like a single image can make him go crazy. I think Nico might have a few anxiety issues, but he's not some little depressed dude who can kill people with the snap of their fingers. He has strengths and weaknesses, and you should not romanticize his conditions. I'd prefer if you just stayed canon, but it does add to the story if you portray it right.

For example, @Sparrow-_-2020 (Sparrow-_-2020) gave Nico an eating disorder. It explains things, it's not at all romanticized, and it advances the plot. You should really check that account out, if you like Nico di Angelo crossovers.