Kiriko Tsujimori was part of a team of J.S.D.F. soldiers sent into Osaka in 1996 to combat Godzilla. Armed with only rocket launchers, the platoon was easily crushed by Godzilla. Enraged by the loss of her comrades, Kiriko fired several rockets directly at Godzilla, drawing his attention. As Godzilla approached Kiriko, her commander, Takuya Miyagawa, ordered her to retreat immediately. Kiriko refused and attempted to fire another rocket at Godzilla. Miyagawa saw Godzilla destroy a nearby building, causing large chunks of rubble fall toward Kiriko. He pushed Kiriko out of the way, and was buried under the rubble, killing him. Kiriko solemnly picked up her fallen commander's dog-tag, and screamed defiantly at Godzilla, firing another rocket at him.
Five years later, Kiriko was now a major in the J.S.D.F. and was appointed as one of the leaders of the G-Graspers, an elite team of anti-Godzilla military operatives. Kiriko dedicated her career to destroying Godzilla and avenging her commander and other fallen comrades. Kiriko was responsible for recruiting skilled inventor Hajime Kudo to the team in order to help in constructing their new ultimate weapon, the Dimension Tide, a miniature black hole gun that would trap Godzilla in another dimension for all eternity. Kiriko brought Kudo to the G-Graspers' HQ in an abandoned warehouse in Tokyo and introduced him to the various individuals that were part of the operation. After the Dimension Tide was completed, Kiriko was present when it was test-fired at a run-down schoolhouse. Kiriko was alerted when another G-Grasper had caught a young boy snooping near the restricted area. Kiriko confronted the boy, Jun Hayasaka, and informed him that it was alright. She made Jun promise not to speak of what he saw, and then gave him back the insect collection that he had dropped. When Godzilla has been sighted in the waters off Japan, Kiriko and some other G-Graspers flew to his last known location in a GX-813 Griffon, where they found the corpse of a giant dragonfly floating in the water. Godzilla suddenly surfaced, and Kiriko was knocked off of the raft she was on. Kiriko grabbed onto one of Godzilla's dorsal plates and rode on him as he swam, managing to plant a tracer bullet on his back. When Godzilla submerged again, Kiriko was rescued by the Griffon and taken back to G-Grasper HQ. Kiriko was told to meet with Jun Hayasaka again, as he supposedly had information about the giant dragonfly she found earlier as well as several brutal killings that had occurred in Tokyo's Shibuya district. Kiriko mat with Jun, who seemed remorseful and guilty. Jun revealed to Kiriko that he had found a gigantic egg left behind by a giant dragonfly that then flew into a wormhole left behind by the Dimension Tide's test firing. Jun had dumped the egg into the sewers below Shibuya where it hatched into several Meganulons, giant dragonfly larvae from the Carboniferous period that transformed into Meganula. Kiriko assured Jun that it wasn't his fault, and then returned to G-Grasper HQ.
The Dimension Tide was ready, and Kiriko and two other G-Graspers were sent to Kiganjima in a Griffon to lure Godzilla ashore so it could be fired. After the Griffon had lured Godzilla onto the island, a swarm of Meganula flew overhead and attacked Godzilla, making the Dimension Tide impossible to aim at Godzilla. After Godzilla had killed some of the Meganula, the Dimension Tide was fired, and appeared to have been successful. However, Godzilla rose from underneath several rocks and returned to the sea, unharmed, much to Kiriko's dismay. After the Dimension Tide had been repaired and readied to fire again, Godzilla suddenly surfaced in Tokyo Bay. Kiriko was sent to intercept Godzilla in the Griffon and hopefully lure him away from the city, but Kirko noticed that Godzilla was staring at something above the Griffon. Suddenly, the Griffon's controls failed, and Megaguirus, the Meganula queen, flew past the ship and attacked Godzilla. As the two monsters battled, the Griffon made an emergency landing on a nearby rooftop. Kiriko rendezvoused with Motohiko Sugiura and Dr. Yoshizawa on a rooftop, and discovered that Godzilla was after a plasma reactor housed in a science institute, even though plasma energy had been banned after it attracted Godzilla to Osaka in 1996. Kiriko was enraged that Suguira had lied and allowed so many people to die, and struck him across the face. Kiriko was then contacted by Kudo, who told her that the Dimension Tide was active but falling out of orbit and unable to lock onto Godzilla. Kiriko returned to the Griffon and flew it over Godzilla, allowing the Dimension Tide to lock onto it. Kiriko then jumped out of the ship and parachuted into a nearby swimming pool. The Griffon crashed onto Godzilla, and the Dimension Tide was fired. Godzilla disappeared, and the mission was declared a success.
A few weeks later, Kiriko tracked down Kudo and told him that he was needed again, as there was seismic activity under Tokyo and it was feared that Godzilla might have escaped the black hole. Kudo refused, saying that he was done fighting Godzilla. Kiriko playfully punched him in the arm, causing Kudo to yelp in pain, as it was the same arm he had broken earlier. Kiriko apologized to Kudo and laughed.
- Kiriko Tsujimori is very similar to the character Akane Yashiro from Godzilla Against MechaGodzilla. Both are members of the J.S.D.F. who lost their comrades in a battle against Godzilla in the past, and hold a grudge against Godzilla and play an important role in an anti-Godzilla operation. This is most likely more than coincidence, as both Godzilla vs. Megaguirus and Godzilla Against MechaGodzilla were directed by Masaaki Tezuka.