Saiga are elemental weapons created by divine power and are manifestations of the wielder's soul. Saiga can take on an element based upon which element the Buster is most skilled with. They are usually the most powerful weapon in the buster's arsenal (except for Zenon and Beet who have the ability to erode their bodies in return for even greater power).
Saiga consume alot of power and so can only be brought out for short amounts of time. If the saiga is manifested for too long, the Buster will lose consciousness and the saiga will return to him. Also, if the Saiga is damaged, the Buster will sustain damage as well.