An experimental satellite-based weapon that fires miniature black hole, called the Dimension Tide, opens a wormhole through which a prehistoric dragonfly enters the present and deposits a single egg before exiting through the wormhole. A boy finds the egg and takes it with him when he moves to Tokyo. The egg starts oozing a strange liquid, so the boy throws the egg in the sewer. The egg, actually a mass of hundreds of eggs, splits up and starts growing when exposed to water, hatching into large dragonfly larva called Meganulon that come out of the sewer to feed. They flood a portion of the city and moult on the sides of buildings, becoming adult Meganula.
Meanwhile, the atomic dinosaur Godzilla appears, in search of a source of nuclear energy, despite the edict shutting down all such attractants after his three previous appearances. While Godzilla is fighting the G-Graspers (the anti-Godzilla section of the Japan Self Defense Forces) who are assisted by rebellious scientist Hajime Kudo, the swarm of Meganula are attracted in turn to Godzilla's energy, and attack him. Most Meganula are killed, but a few drain some of Godzilla's energy and return to the sewer. With the last of their strength, the Meganula inject Godzilla's energy into a huge, sleeping larva that is in a giant, pulsating cocoon. It molts and appears from the water as Megaguirus, the queen of the Meganula.
After destroying part of the city with shock waves generated by her beating wings, Megaguirus heads to the waterfront and faces Godzilla. Being territorial, Megaguirus considers the city to be her hunting ground. As they engage in a lengthy battle, she uses her speed to avoid Godzilla's attacks, but Godzilla eventually uses her speed against her. As she flies toward Godzilla, he lunges forward with his dorsal fins in her path. She flies into the fins, and one of her arms is severed.
During the battle, a special ability of Megaguirus is revealed: Having been mutated by Godzilla's energy, she can generate a blast similar to his atomic breath. She fires a huge ball of radiation, knocking Godzilla down. He gets back up, and Megaguirus goes in for the kill. She speeds forward with the stinger on her long tail lowered, trying to stab Godzilla between the eyes. In a climactic moment, Godzilla catches the stinger in his mouth. He bites down, crushing the stinger. Megaguirus rears up in pain, and Godzilla takes the chance to finally blast her with his atomic breath. She bursts into flame and Godzilla blasts her a second time and destroys her.
It is revealed that Godzilla was attracted to the energy of a secret nuclear project housed at the Science Institute, in violation of the ban, by Professor Yoshino Yoshizawa. The G-Graspers are now wanting to kill Godzilla, but with the Dimension Tide falling out of [[Wikipedia:Orbit|orbit] they are unable to get a lock on Godzilla, until the beautiful and psychotic Major Kiriko Tsujimori pilots a ship called Gryphon towards Godzilla, ejecting only at the last second. The Dimension Tide is able to lock on to the craft and fires just before burning up on reentry; Godzilla vanishes and everyone celebrates. In a postlude, however, Major Tsujimori again enlists Kudo to investigate suspicious seismic activity; then in an after-credits scene, Godzilla's roar is heard again as an earthquake strikes Tokyo.
The cast of Godzilla vs. Megaguirus are predominantly new faces to the Godzilla series, but the film began a tradition in the Millennium series of casting veteran genre cast members, especially from the Showa era, in older, authoritarian roles: Yuriko Hoshi, who played photographer Junko in Mothra vs. Godzilla and reporter Naoko in Ghidorah, the Three-Headed Monster, cameos as Professor Yoshizawa, director of the Dimension Tide project.
- Misato Tanaka as Kiriko Tsujimori
- Shosuke Tanihara as Hajime Kudo
- Masatoh Eve as Motohiko Sugiura
- Yuriko Hoshi as Prof. Yoshino Yoshizawa
- Toshiyuki Nagashima as Takuji Miyagawa
- Tsutomu Kitagawa as Godzilla
- Minoru Watanabe as Megaguirus
The budget of Godzilla vs. Megaguirus is estimated at $8,300,000. It opened in Japan on December 16, 2000, and during its box office run, it grossed approximately $10,000,000, making it the second lowest-grossing entry in the Millennium Godzilla series. Total admissions in Japan were approximately $1,350,000.
The reaction to Godzilla vs. Megaguirus has been mixed. Ed Godziszewski of Monster Zero said, "While not the best example of filmmaking, Godzilla vs. Megaguirus nonetheless succeeds as an entertaining film." Miles Imhoff of Toho Kingdom said, "Run-of-the-mill, mediocre, and sterile are the three words that best describe Godzilla vs. Megaguirus. It is a movie that attempts to be creative and edgy, but somehow fails, leaving one wanting with futility to really try to enjoy the film."
Stomp Tokyo said "the music is pretty good" but "this movie isn't a step forward in the ways that it really should be." Mike Bogue of American Kaiju said, "Though not the best of the post-Showa Godzilla movies, Godzilla vs. Megaguirus is one of the most entertaining." Ian Jane of DVD Talk said, "While not the best entry in the Godzilla series, Godzilla vs. Megaguirus ... [is] still a really solid entry with some great special effects and a very memorable monster mash finale."
Matt Paprocki of Blog Critics called the film "a true classic in the series," adding: "It's impossible not to be entertained somewhat, whether you're looking for camp value or serious giant monster action. This one has everything that is required of the kaiju genre." Andrew Pragasam of The Spinning Image called the film a "flawed, but entertaining comic book extravaganza" that "only partially delivers as a slam-bang monster epic" and suffers from "a lack of likeable characters."
- Released: January 27, 2004
- Aspect Ratio: Widescreen (2.35:1) anamorphic
- Sound: Japanese (5.1), English (5.1)
- Supplements: Trailers for the American Godzilla film, The Medallion, Alien Hunter, Returner, and So Close
- Megaguirus and the Meganula are both adapted from the man-eating insect Meganulon which first appeared in the 1956 film, Rodan.
- The opening footage of the film which flashes back to Godzilla's first attack on Tokyo is actually footage from the original Godzilla film with the new Godzilla suit, GiraGoji, digitally edited in.
- In this continuity, Godzilla was not destroyed by the Oxygen Destroyer, but instead, attacked Tokyo and retreated into the ocean, never to be seen again until 1966. That makes this film, as stated above, the only Godzilla film not in the same continuity as the original.
- This was the last Godzilla movie where the Godzilla suit has a greenish tint.