Silha is a mysterious island and a key location in the Guyver manga. This small landmass remains hidden from human civilisation, with only a handful of individuals within Cronos possessing any knowledge of its existence. During the Creation period, the Ouranus landed one of their bio-ships here and the area became one of their primary bio-weapon test beds on Earth. When they left Earth, the ship located here was abandoned in favour of a newer, more efficient design, but some of its systems remained functional. Afflicted with a lethargic condition by his Creators, the Zoalord Archanfel turned this island into his own private sanctuary where he could rejuvenate himself, entering stasis within an amniotic capsule inside the Ouranus vessel. Archanfel maintained psychic contact with the various creatures that were left behind on the island, which constructed a great temple around the Zoalord's inner sanctum.

Silha had been undisturbed for thousands of years since the Creators' flight from Earth. The island is constantly surrounded by an electromagnetic field that disrupts any technology within its radius; storms and vortices fill the surrounding sea, destroying any ships that approach. The only human to discover the island was Dr. Hamilcar Barcas (before he was known as such) 400 years before the events of the Guyver series take place. He miraculously survived the destruction of his ship and became stranded on the island, finding it inhabited by all manner of abnormal creatures: giant dragonflies, dinosaurs, even mermaids. As he explored the lush jungles of the island, he came across the temple where Archanfel resided, finding him in suspended animation within an amniotic pod. Barcas immediately found himself in awe of Archanfel and pledged his allegiance to him. Since then, Archanfel and Barcas founded the secret society of Cronos and worked toward the transformation of the entire human race.

To date, the only people on Earth aware of Silha's existence are Archanfel, Dr. Barcas and the two loyalist Zoalords Sin Rubeo Amniculus and Friedrich von Purgstall. Recently, Sho Fukamachi's friends Tetsuro and Mizuki Segawa have found themselves dumped within Archanfel's temple on Silha after being abducted the mysterious being known as Apollon.