The Guyver is a manga written by Yoshiki Takaya. The Guyver itself is a symbiotic techno-organic (or biomechanical) device that enhances the capabilities of its host.
The series has two OVA's which where Out of Control in 1986 and The Guyver - Bio-Booster Armor in 1988. In 2005 it had it own anime series adapting chapters 1 - 59 (volume 10) of the manga.
There are also two live action movies that came out in the early 90's which are not too good critically speaking, but the second movie is a pretty decent flick.
Power of the Verse
Guyver is a fairly powerful verse. Especially with Alkanphel (a small planet buster in his own right), several characters who can easily destroy cities, several characters with massively hypersonic speed and relativistic reaction times, some powerful broken abilities to boot, and nukes.