[FairyKing]

I haven't fully fleshed this idea out, but there was some discussion here a while back about Kamen Rider giving people hope, and elsewhere about the potential for a toku isekai, so that got me thinking about a Kamen Rider helping people survive and rebuild in a post-apocalyptic future. I call it Kamen Rider Ruin, and the tagline is "the future lies in Ruin."

Our hero is a delivery man from the modern day who brings a package to a science lab, but gets caught in an attack by some unknown enemy and ends up getting cryogenically frozen with the package. He thaws out 100 years into the future, where people live in domed cities to protect themselves from Maelstroms, bizarre natural disasters that mutate anything caught in them into monsters called Mal. Kamen Riders travel between the domes to deliver mail and packages, gather resources only found outside, and protect other travelers from the Mal. As fate would have it, the package our hero was carrying contains a powerful prototype Driver, and he becomes a Kamen Rider to help people and try to uncover the mystery of what happened 100 years ago, clashing with Mal and human villains who want to conquer the surviving cities.

The collectible items are Storm Filters, lenses themed after different natural disasters that attach over a light on the Driver and equip different protective gear onto the Riders' base suits (this Rider system was originally designed as advanced safety gear that could adapt to different dangers). Creating one requires disaster data either copied from another Storm Lens or gathered directly from a Maelstrom.
Ruin starts with the Cyclone Storm Lens for his main form, later gains Lightning and Blizzard lenses, the powerful Typhoon lens passed on from a veteran Rider who becomes his mentor, and finally the Perfect Storm Lens from going all the way into the eye of a Maelstrom.

The Mal are creatures that survived unprotected exposure to a Maelstrom and came out of it mutated with monstrous new forms, strange abilities, and an urge to destroy. Most are mutated from animals and are just mindless beasts, but those mutated from humans are unique and keep their sentience. Some of these human-Mal are evil, but there are also those who don't want to hurt anyone and find ways to control their destructive urges.

I don't know who the second and third Riders are (maybe Ruin's mentor should be one of them?), I figure since in this post-apocalyptic world being a Kamen Rider is just a job there would be a large number of them, and they might just use their real names as their Rider names, like Horobi and Jin. And there's probably multiple Riders with duplicates of the same Storm Lens, or else ones that are very similar (Cyclone and Tornado, for example). Maybe the second Rider should use Volcano for their main form, that seems like a good contrast to Ruin's wind- and sky-based forms.