Millennium

Godzilla Against Mechagodzilla and Godzilla: Tokyo S.O.S. - These two films are the only entries in the Millennium series to share continuity, and are often collectively referred to as the "Kiryu Saga." Godzilla Against Mechagodzilla is a direct sequel to the original Godzilla and establishes that Godzilla first appeared in 1954 and was killed by the Oxygen Destroyer. The only change from the events of the original film is that Godzilla's skeleton remained intact instead of being disintegrated. This film also references the events of Mothra and The War of the Gargantuas, including stock footage from both films. The next film, Godzilla: Tokyo S.O.S. is a direct sequel to Godzilla Against Mechagodzilla and makes further references to Mothra, even featuring the character Shinichi Chujo. The events of the film Space Amoeba are also referenced when the corpse of Kamoebas is found on a beach. It is also mentioned that another Kamoebas was seen sometime in the 1980's. Supplementary books for the film establish that the events of several other non-Godzilla Showa era kaiju films occurred in this continuity, including Rodan, Varan, Gorath, Atragon, Dogora, Frankenstein vs. Baragon, and King Kong Escapes.