Why was Nico at the Senate meetings?

Question

In The Son of Neptune, we see that Nico di Angelo, as the 'Ambassador of Pluto', joins in the Senate's meetings:

Reyna and Octavian led the procession of senators out of camp, with Reyna's metal greyhounds dashing back and forth along the road. Hazel, Frank and Percy trailed behind. Percy noticed Nico di Angelo in the group, wearing a black toga and talking with Gwen, who looked a little pale but surprisingly good considering she'd been dead the night before.
[...]
The senators passed through easily. The statue checked the tattoos on their forearms and called each senator by name.
"Gwendolyn, senator, Fifth Cohort, yes. Nico di Angelo, ambassador of Pluto - very well. Reyna, praetor, of course. Hank, senator, Third Cohort - oh, nice shoes, Hank! Ah, who have we here?"
_{The Heroes of Olympus, book 2: The Son of Neptune, chapter 13}

Why does Nico come to the meetings? He's not a senator, he's not even always at Camp Jupiter. Why is he allowed to take part in the running of the camp like this?

Answer 1

1. Pluto is the god of death and wealth. Both things that are respected - the former with a good deal of fear. This is a representative of that god. Treat them nicely.

2. Considering the stuff that's happening with the Doors of Death, etc, which Reyna knows about as evidenced by her talk with Percy before he leaves on his quest, a guy who's an expert on death could come in handy - like, I dunno, the son of Pluto? The Senate hears from Nico on what the distinction between the Doors of Death, Thanatos, Pluto, etc, is.

3. Nico is kind of a scary kid. Fitting with #1 - you do what the powerful kid who can bring skeletons up from the ground says to do.

4. Nico is an ambassador. Ambassadors are generally offered that sort of courtesy, both in the real world and in the Jackson-verse.

5. Nico knew the importance of what was going on. He had several big tickets on his plate - first, going with #2, protect the Roman camp and keep it informed. Next, to keep Percy safe on his quest. (Remember...that crush is still slightly in play as well.) Next, keep his sister safe, which involves trying to control how the quest she's going on is set up. Next, keep eyes on both the Greek and Roman camps, which his dad, the scary god of death, ordered him to do. All of these things require him to be at the meeting. He knows what's at stake, he's going to get in there no matter what it takes.

6. Finally, there's the camp politics. I don't have the books handy, but if I recall aright, in Book 5, when Nico's taking the statue back and goes all explode-y on the one kid who's trying to stop them, it's implied that Octavian wouldn't mind Nico's power on his side. I mean, heck, who doesn't want the powerful Big Three child on their side? So Octavian who's trying to get power wants to get Nico on his side, and one way to do that is show that they "trust" Nico by letting them in on the important meeting. Further, Reyna also sort of trusts Nico, so she has even more motivation beyond #2 to get him in the meeting.

Answer 2

Hades/Pluto gave Nico knowledge of both camps and responsibility for watching over them. This is explained over the course of the book, and the next one, through conversations with Percy and Hazel.