This artist is VERY similar to the hentai artist Tamahagane, so similar that I almost suspect it may legit be the same person with a different alias.
This is the least explicit example of their art I could find, but it still NSFW so you have been warned( no nudity, a girl in her underwear)
Apparently I am not the only one who suspects this is the SFW alias of Tamahagane, the mangaupdates profile of the mangaka says the same thing.
https://www.mangaupdates.com/author/gyh5e9n/asakura-maru
Knowing this is likely Tamahagane makes this story make a lot of sense to me.
They are a huge exhibitionist genre artist, with pretty much every hentai of theirs being about nudism and exhibitionist fetish, so I bet that here, the magical girls gain their powers from exhibitionist activities.