Name is Kamen Rider Dragoon. Think you can do something like a cross between the Arquebusiers and Papal Guards from Assassin's Creed?
Basically, the front section slides straight down to form the breastplate, the back and top move in a similar manner to form a cape, and the two sides fold into themselves vertically to form the "sleeves".
I think you suggested having some of the exposed internals a dark red, so that could probably count for the visor and cape inner lining. The "mowhawk"/crest on the helm would be green to look like the stem.