Friendship and Giant Eyebrows.

OOO: Desire and Alchemy

Dopamine triggers reactions that cause particles to be super-charged with enough energy to create tachyons, which in turn create rifts in the space-time continuum which release either Cell Medals from an infinite set of realities where when matter from another reality enters, it is shot back and multiplied (more dopamine meaning more energy to charge particles in Cell Medals to shoot back and forth); or releasing OOO's armor.

And suspenders:lol

In addition, proteins that compose the hair that make up eyebrows are temporarily broken down to be used as energy for minor tasks the suits have to do, creating a 100% efficient machine, before they are re-constructed back on the donor.

Suspenders: Elastic Potential Energy->Sound and Kinetic Energy.

I always saw 000's power coming out as condesned energy released into greater energy.

The Coins could be considered batteries. Each one holding an animals condensed energies, or spirit. Which combined, in a specific order, released the energy inside. Long as you have a Henshin to control and harness the energies. Otherwise you end up with a Greeed. (Sorry if I messed that one up Lol)

While his emotions controlled the abilites of each form, much like an animal.

But with Kamen Rider, and Sentai/Power Rangers, I always saw each of them needing a little magic to transform. For lack of a better word. Except for something like Lightspeed Rescue, which was more tech.

Again, much like my theory of tachyons.

By the way, I have to take back what I said about other non-Kamen Rider series by order of CookSux. But since the "magic" you refer to, in a Sentai series, it would just be part of the laws of physics, since different realities would potentially have different creations. As for Power Rangers; tachyons. They're able to exceed light-speed, therefore they can cross throughout the multi-verse (or "10th Fabric", as I call it). As such, they'd eventually reach a reality where if an object from the Power Rangers' reality comes into contact with it, they grant it special properties, like the actual powers.

Sounds like magic to me. What causes the energy to re-construct back to the donor once it's been used?

Since the mechanism that deconstructs and converts the eyebrow into energy inserts it into a 100% efficient system, the math says that there would be a way to reconstruct the eyebrow back into its matter form (that math being E/C²=M). Either that, or there is no reconstruction involved as the process is too difficult, but only a small amount of eyebrow is actually taken, so small the naked and untrained eye would be unable to notice. Since the system would still be 100% efficient, there would be no need to release the energy it already has stored.

This is, of course, assuming eyebrows are used at all.

every time he snaps his suspenders, an angel gets its wings