For 2004, the closure of Fuji Speedway as part of a Hermann Tilke redesign of the circuit forced the series to move. As a result, four races were held at the road course of Twin Ring Motegi, as well as one at Sportsland Sugo. Hiroki Saga, driving for MYG, won four races on the way to the title, with the other race being won by Nova Engineering's Katsuaki Kubota. However, the entry list had decreased, with no more than five drivers competing in any of the races. Fuji Speedway reopened in 2005, and the GC-21 series returned there for all five races of the season. Team I Line's Hiroaki Ishiura was dominant, winning all five races.
