The RaishuGaru's name comes from Rebirth of Mothra III's Japanese title, specifically raishū (来襲?), meaning attacks, and Garu which comes from Garu Garu's name.
RaishuGaru is very different from the ShodaiGaru. Its head seems to be held up with tubes protruding from its neck. Its wings are held up by pistons, and have lost their cannons. Its upper body is completely mechanical, along with its forelegs.