I vaguely remember seeing the Guyver movie many years ago. It’s one claim to fame was that it starred Mark Hamill. And even that was rather forgettable.
Back to anime: The Guyver is a bionic exoskeleton that gives its wearer superpowers. And the wearer will need those powers because an organization named Chronos has decided that humanity was created to evolve into super-soldiers (by some long-lost space-faring civilization) and they are going to accelerate that evolution by creating Zoanoids. Zoanoids first appear as ordinary humans on steroids, but when they get angry they transform into monstrous, mindless killing machines. (There appear to be a limited set of Zoanoid types, so the animators can reuse the cells from previous fights.)
Chronos also found/developed the Guyver suits. They had three of them but they were stolen. In the process of recovering them, one was found by a high school kid, Sho; one was broken; and the other was found by a mystery man. (Well, we all know who he was, but he is supposed to be mysterious) So, Sho is taken over by the Guyver suit and fights the Zoanoids while he learns what the suit can do. The Mystery man appears at times to help out. The MM seems to have a grudge against Chronos as well. And the two of them manage to destroy the Japanese branch office.
Chronos is a global organization, so there are other branches to destroy, if they want to.
And, of course, there is a background high-school story going on. And everyone seems to know that Sho is the Guyver, so Chronos can attack his friends, his school, and anyone else they want. Nothing like wanton, mindless violence to illuminate the meaning of life.
This one is pretty lame all around, so I will give it a 4 out of ten.