I'd get very questioning about why the person wanted it, because the overtness of superheroes stands against the intended game mode of hidden-supernatural urban fantasy of the nWoD. IMO, it's not really the nWoD if the supernatural isn't hiding.
But given I was being paid for it, I'd shrug and then turn superheroes into a thing about celebrity, and how it makes the celebrity less real because their image in the thoughts of others is something manufactured. The superhero is an idea, and thus your superhero form exists only as an idea. You'll never get recognised for who you "really" are, because it's "not real" - but your superhero identity will bleed into the culture and people will copy it without knowing. And it's so easy to give up to the demands of the idea that others have of you, and stop living in the real world, only existing in a way that others can see you for medicinal reasons, losing all your friends and your contacts with normal people as you embrace the heady life of the superhero.
plus i'd probably just make the antagonist splats capeshit that wants to grab you and pull you into the realm of ideas and never let you go, recycling you time and time again and grafting your supehero personality onto someone new when your mortal shell dies
there's probably two of those big bads
they're probably controlled/generated by mortal corporations who might not even know how they're warping the world of ideas
The other angle is to throw this one Monte Cook setting book into a meat grinder and harvest its vital essence.
"Superheroes" are people who start perceiving a supernatural aura that random objects passively emit, and are overcome with an urge to collect articles of such mystically-active junk. Once a critical mass of material is acquired, they black out and awaken to find that they've assembled their magical tchotchkes into a mask - considering the "junk" part of that phrase is paramount, these masks are usually rather odd-looking (one example is made of tape casette ribbons, hairpins, and carved-up book covers, with tufts of Troll doll hair for decoration).
When you put the mask on, "you" end, and a Hero begins. It's a piece of who you are, but bigger, louder,
more. The Hero takes one of your core personality traits and then cranks up the contrast until it's unrecognizable, creating an alien caricature that then gets garbled even further by lingering traces of the disparate talismans you ripped apart to make your mask.
A happy-go-lucky jock might end up with a Hero form that embodies his physicality, with rippling, grotesque muscles barely restrained by a too-bright replica of his varsity jacket, and a sledgehammer where its face should be. On the other hand, his mask might birth a capricious, anarchistic Bacchus with stage light eyes and a hallucinogenic aura that smells like the turf on the football field - hungry to feel and live and experience, and oblivious to how it drags people near it into its insane revelry.
Heroes aren't usually stable, or peaceable, or even particularly smart, but they're powerful, oh so very powerful, and you always remember the cool parts of what you do as a Hero better than the... other parts.
Eventually, you might realize the human cost of your new hobby, but by then the Hero's been allowed to breathe, gotten used to living outside of your cramped little skull. It doesn't want to go: if you stop being its sidekick, it'll get grumpy, and then it might think about making a mask of its own. After all, you're so boring and dull! Shouldn't
you be the one that has to ride shotgun?
Also, Heroes naturally attract each other, and once two Heroes become allies - or rivals, or secret lovers, or mortal enemies - their human "owners" find it even harder to put down the mask for good, because now they have to worry about the other guy's Hero coming after their "secret identity" and trying to force their Hero back to the surface.
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To be a bit more Doylist, the "superheroes" are people who've become some sort of
hithimu-equivalent entity - a "Hero" is an inhuman force driven by human motives/concepts, taking something their host cares about, or something they hate, and then "dealing with it" in an utterly unhinged fashion. They're a satire of the inherent psychological weirdness of how comic book characters often try to use costumed capers to accomplish goals that would be better accomplished in a less flamboyant fashion. They try to reduce complex problems into something they can solve with their fists, and everything that happens around them is either meaningless background scenery or a new component of their narrative.
Heroes are the new Olympians, and like the Olympians, they're capricious madgods who can drop out of the sky and tear down your world at any moment, yet demand acclaim and consider themselves paragons of virtue.
