Roger and Brenda’s skepticism makes me wonder. How common are obvious manifestations of powers?

Well, it really depends on where you live. It's obviously not as common place as MHA for the more fantastical powers, but it's common enough that, (spoiler for the next page) people are more likely to make the accusation that it's someone with a Nature pulling a prank, rather than a ghost.

In fact, Calypsia's version of "police" (at this point in the timeline) aren't even the ones who have to deal with the more fantastical criminals. And unlike MHA Furs are allowed to use whatever they have to protect themselves and others. For example if you have strength, you can smash wall out to escape a fire. However... how to put this nicely.... "user digression is advised". Using the same example, you may be held accountable of damages done to the building should you smash willy nilly, even WITH lives on the line.

Mind you, remember, this story wont have any big epic fights, thus no big epic Natures/Powers to go along with it.
Even came up with a decent name for Roger's ability... and then I also realized the accidental pun that comes along with it.

Yeah, that’s what I was getting at, if it’s common enough that any odd occurrence, like a “ghost sighting” might be attributed to a Nature by regular people. So, it’s not as common as the 80% in MHA, but is it like most people know someone whose Nature has manifested.
“Oh yeah, my brother-in-law can levitate.”

Though I do like the idea superheroes and such being accountable for collateral damage. I imagine insurance policies have to have some paragraphs dealing with Natures.

Well, i guess it's a bit more like finding someone who can bend their elbow backwards, or can curl their tongue or pop their eyes out of their sockets (the record is a full inch). It's not unheard of but still kind of freaky when you see it.
Fun fact: I actually knew a girl who couldn't lick ice cream (or anything really) because her tongue was barely too short to reach her own lips.

In the much earlier days (and I guess in specific cities), it's actually required for Furries to wear a type of inhibitors (if I recall correctly) are called "catalysts". They make Furs look take on their human appearance and prevents them from using Natures. It was done as a security measure at first, (and yes, it was abused). It's still one of the easiest way to prove you weren't involved in something is to just present that your Catalyst was active at the time. In this the story world, most don't need them anymore and they're purely optional.

So I guess you can think of them like the quirk canceling cuffs from MHA or, the Epithet erasing cuffs from Epithet Erased, or the SeaStone cuffs from One Piece... sure are a ton of these cuff things, huh?

Collars have been used in some DC settings. Also Is it bad I haven’t seen One Piece?

They have to deal with MetaHumans somehow, even if it's by "magic" power inhibitors.

No, but now's a really bad to time to get started. You thought that the K&K archive dive was bad...? It's currently at 1016 chapters and still growing. Brightside, you'd only have to watch every other episode of the anime as they tend to review half of the previous episode with the entire first half of the next. Mind you, that's full chapters, not just strips.

All you really need to know to understand the reference. Is that (the main source of) the super powers are granted by eating Devil Fruit, but in exchange you won't be able to swim in salt water. (In actuality it's more like paralysis.) Thus the sea stones radiate "the ocean's aura" which naturally negates Devil Fruit powers without completely paralyzing them.

Yeah, that sort of thing is why I haven't tried tackling a number of long-running webcomics (or other series for that matter). Might look into TwoKinds and/or Housepets at some point.

Both of those are much easier as they updated much less frequently over the years.

Even I find trouble not to go through the entire history, once I get started myself.