So (among the way too many unfinished and unpublished fanfics I've been working on) I kinda started making rough drafts and outlines for a crossover fanfic where a ton of franchises exist in the same world, and have them go against a rogue AI known as the Hive and you can probably figure out where that's all heading.
Anyway, I was planning that the story starts with the Kim Possible, Carmen Sandiego (2019), Totally Spies characters cause I feel those 3 universes can fit together easily enough and it's a smaller scale to start the story at.

My two things I'm looking for advice on are:

1) Which other franchises should I include (and why)? I'm trying to have it be modern/ advanced world setting so I'd rather magic and fantasy...though I guess superheroes might work.

2) Who should I start the story with? I really can't decide between Kim, Carmen, Clover, Sam, or Alex. I wrote the opening to just be open to any single female character really. Basically whoever I start the story with is going to get corrupted immediately while other characters get to remain good guys....for at least a bit longer...

edit: My general plan is have start with these 3 universes, let the character's fates play out (some, but not all, get corrupted), then introduce next set of franchise's characters and the remaining good guys meet those characters and repeat.

Anyway, love to hear thoughts on this.

additional edit: Here's the rough outline of the starting point of the story for context
So Character A receives a package or email that when opened turns out to be a hypnotic virus that infects their computer and subliminally conditions them to get lured to a Hive facility where they get converted into a sleeper agent for the Hive (and also prior to that, the Hive flexes and shows off the different types of drones and forms of brainwashing they have to her, and demonstrates on some women like maybe Bonnie from KP or Mandy from TS or maybe even April O'Neil, you can throw in your suggestions for who these victims could be). Then from there, the remaining good guys are given reasons to investigate the Hive which leads them trying to sneak in and they run into each other (ofc w/ one being already turned).
So like I said, it doesn't matter too much who is the first character, I'm just stuck.

It sounds like you're going more spy fi or spy fi-adjacent, so I'd start there and work outwards.

Well I guess for a starting point but I was asking for franchise suggestions cause I'm kinda brain farting on them

(edit: I chose those 'spy fi' characters mainly because I need characters that both would and could sneak inside a Hive facility, the rest of the story doesn't have to stay limited to that sub-genre, just at least be compatible with it...like maybe My Life as a Teenage Robot could work too but I'm debating if ones like Teen Titans or Overwatch would work)

If you ask me, I would say one of the totally spies. I feel if you'd want to raise the stakes for another character, you'd need someone who they're close with to take them down and in a crossover, familarity is important. Plus there's more potental for interactions with an evil totally spies member.

As for who should be taken down, I will admit I'm not familar with the series but Sam seems the most logical option from an outside perspective as I think she's more of the leader type from what I've seen.

Anyway cool idea.

I guess it depends how graphically consistent you want to be with this. I mean if we're talking children's sci-fi/agent-type franchises, there's a numerous amount of TV series featuring "real" actors - I have to assume, though, that you're intending on more of a cartoon, maybe 3D animation, maybe video game -type deal, given your suggestions up to now.

With that in mind, here are some series that, depending on the atmosphere you'd want to achieve and how far you're willing to stretch the "shared universe" concept, could maybe work (shamelessly ripped from the <<mentalblock.miraheze.org/wiki/Category:Western_Cartoon|"Western Cartoon" category>> over on Mental Block):

-Amazing Spiez (Totally Spies' lesser, and lesser-known, cousin/spinoff - as such, definitely worthy of a mention, given it seems to take place in the same universe);
-Animorphs;
-Ben 10;
-Danny Phantom;
-Darkwing Duck;
-DC Super Hero Girls;
-Dexter's Laboratory;
-DuckTales;
-Fairly OddParents;
-Futurama;
-G.I. Joe: A Real American Hero (and any associated works, such as Renegades);
-Gravity Falls;
-Grim Adventures of Billy and Mandy;
-Pixar's Incredibles;
-Invader Zim;
-Inspector Gadget/Gadget and the Gadegtinis;
-Jimmy Neutron;
-Johnny Test;
-Martin Mistery;
-Max Steel;
-Mega Man;
-Mysticons;
-Phineas and Ferb;
-Pinky and the Brain;
-Powerpuff Girls;
-Rambo: The Force of Freedom;
-Real Ghostbusters;
-ReBoot;
-Rick and Morty;
-Scooby-Doo;
-Sonic;
-Steven Universe;
-Super Friends;
-Team Galaxy;
-Teenage Mutant Ninja Turtles;
-Transformers;
-W.I.T.C.H.;
-Winx Club;

+ any number of the animated series featuring sci-fi hero teams and/or super-heroes not mentioned above, such as Iron Man, Batman, ThunderCats, He-Man, X-Men, Shazam, Bionic Six, Challenge of the GoBots, etc.

In terms of video games, I don't really have anything off the top of my head, but I'd suggest maybe looking at anything sci-fi or sci-fi adjacent, with memorable characters, such as Overwatch that you mentioned above, or Cyperbunk 2077, or maybe some action-adventures from before (like Metroid or Crash Bandicoot) or any fighting game series like Street Fighter.

I wasn't trying to be 'just' western kids cartoons, it's just what I got stuck since this idea started cause I saw a hypno crossover story prompt involving Kim Possible, my mind went straight to mashing it up with Totally Spies and Carmen Sandiego for the reasons I already gave.

I do appreciate the list, it helped me recognize what I was looking for/what I wasn't. Like with the super natural, superpowered characters like Supergirl or Emma Frost I feel are reasonable but I'm very iffy about Zatanna cause she's full on magic and Raven (even though I love her) is a demon.

But also, I don't have to overcomplicate things and I could just cherrypick characters instead of trying to bring in the entire franchise, like say Vicky from Fairly Odd Parents cause while there is magic all around her, she can't use it and more importantly, is completely oblivious to it. Probably won't actually use her, just an example.

I agree with what you said, which is why I already had a general plan for how one of the spies would betray the others. It's just that one of the spies doesn't have to get converted right away. And like if say I start the story with Kim, it would give the audience that dramatic irony of when she 'conveniently bumps into' the spies, that its not at all a coincidence. It's like I see benefits to each character being this sacrificial lamb to start the story, but am wracked with indecision because it'll mean that that actual character will be done for the rest of the story because it'll be an evil version in their place (which granted will be the fate for a lot of characters and its the dilemma of when do I pull the trigger for each of them)