Another Ponyville is under siege by a swarm of Worm-like changelings, and only one hero can stop them. The one name in this world you need to remember. Shining in the sky after every storm, a speed faster than your eyes. Rainbow. Dash.
(Henshin One-Shot, Kamen Rider Kabuto crossover. Warning: Gen3.5 incoming.)
Better question is how does Fluttershy know that? Unless Equestria has a Kamen Rider rip off, she shouldn't. I kind of skimmed the Kabuto part since I haven't seen it yet.
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The Kabuto part…of the story? The Kabuto part is the story. But really, it only borrows the Rider System and the way the monsters work, no spoilers to be found, if that was the issue. And Fluttershy knew because Rainbow described it like that when she told the story.
Wait, Gen3.5? Isn't that the episodes with the really bad acting and animation?
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Depending on what you’re thinking of, maybe not. Most things pre-Gen 4 had “subpar” animation by some standard. The reeeaaally infamous early Flash-animated demon babies of Newborn Cuties, what’s probably coming to mind, were yes technically part of 3.5, but I call them Gen3.666 instead; the main 3.5, and the one I’m using, was just before that with the likes of Twinkle Wish Adventure. It made everyone look like chibis, which gave me the perfect “civilian form” base for the two-stage Kabuto transformation, which is why I chose it.