From MangaUpdates:

Hoichi Kano, the Grandson of world famous inventor Hosuke Kano, is a student at Howa High School in Musashino City. At the tenth anniversary of the first contact with the Riofaldians, the unveiling of an Elevator Ship designed for orbital transport between the Riofaldian home world and Earth is about to take place. However, this was just a ploy to take control of the Earth using their advanced technology and large Riofaldian work force on Earth to their advantage. It is now up to Hoichi, with the help of Hosuke, his school friend Akane and Isaka, to stop them and save Earth.

There is plenty of mecha mega-robot action, state of the art gunsuits, sexy shape-shifting androids and the reason why the manga is called Cannon God...

But the Riofaldian are one step ahead and they have a plan...

Missing volumes: 5