Just to go full "circle" on this thread, here is a quotation from Fujita Masatake:
The body movement used in aikido is summarized in the expression "enter in one step, and apply the principle of circularity." (irimi issoku, enten no ri). You use your center to enter and displace the opponent's center as much as possible. This is irimi. So the "Fujita theory" means training in a way that thoroughly explores this use of irimi.