Umm... from their fallen people throughout time?

The villains' powers could be to create kaijin via "awakening" dormant DNA. Sources could be anything from fossils, extinct or extant animals, what-have-you. For human kaijus as a short arc, perhaps there's a tribe of human who were descended from that magical toku age where they lived with the dinosaurs and inherited their heritage/whatever.

Any chance for the kaijin to mix dino fossils with humans skeletons?

As for a female kamen rider, perhaps the use of a parasaurolophus?

Fangires killed and ate people on a regular basis (assuming that going translucent was a one-way gig) and every Phantom was once a living person with a life, hopes, dreams, family and friends.

And with Fangires, Rook killed as many people as possible based on some theme within a time limit for FUN.

It doesn't have to be awakening dormant DNA it could instead be by mutating existing DNA like how evolution works

I too kinda want an early heisei tone with the story

I did mean mutating, awakening a cat to its unchanged DNA would be a pretty non-threatening creation wouldn't it? Whatever term you use for it, as I'm not sure on the exact nature of the Extincts. I can only intuit so far that they are beings that have tried to forcible evolve themselves for power. I used awakening because they would see it as a uplifting creature to their true potential.

Let's say that the villain's base is at a site where there are several fossils all around them.

sure why not

anyway Im gonna start sketching the other forms later so heres some thing I plan on implementing on them:

Remember the how Thero has a magnifying glass on his chest? I plan having it on different positions with each form. Pointed northeast for Thero, Southeast for Quad, Southwest for Aqua, Northwest for Aero and Downwards for Omni. Doesn't really have a function, just looks cool

And the ribcage shoulder pad is different for every form.

Thero- Ribcages
Quad- either a large piece of anky armor or triceratops....um...fin thingy
Aqua- Gill-like vents that absorb moisture from the environment
Aero- Feather-like armor
Omni- everything placed on the extremities

this are mostly aesthetic though

what about you guys do you have any ideas you want implemented as well?

and in that same series, we get a touching storyline of two men whose lives were "ruined" by Kurenai cut short because "gotta make the monster super edgy" AFTER they had realized that they liked their lives the way they were. it didn't feel tragic it felt unwarranted and unnecessary.

like, I'm okay with dark elements, but it doesn't need to be super mega ultra dark edgiest of edge kinda thing.

You don't really need to kill people to make a story dark......

You just have to break them and make them suffer *insert innocent smile here*

Wanna hear how I do it :D