Godzilla Junior is a heroic monster, the secondary monster character and overall the tritagonist of the Heisei Godzilla movies. He is the son of Godzilla. In Godzilla vs. Destoroyah, he was killed by Destoroyah in the climax, but he was reborn as an adult Godzilla and took the place of his father so Godzilla's legacy will never end.
Godzilla Junior's appearance changes from film to film as he ages. As Baby Godzilla in Godzilla vs. Mechagodzilla II, Junior stands about human height with a slightly hunched posture, and has bluish skin with a gray underbelly and small gray dorsal plates running down his back. As Little Godzilla in Godzilla vs. SpaceGodzilla, he now stands mostly upright, and has a large head and very large brown eyes and green skin with a yellow underbelly. As Godzilla Junior in Godzilla vs. Destoroyah, he now resembles his adoptive father more closely, with similar body proportions and physical features. However, unlike Godzilla, Junior's skin is green, with a lighter green on his underbelly, his eyes are a light orange color, he has very small dorsal plates on his back, and he stands with a very hunched posture. After absorbing Godzilla's dying radiation and growing into an adult Godzilla, Junior now looks mostly identical to his father.
Godzilla vs. Mechagodzilla II
Baby Godzilla's egg was discovered on Adonoa Island in Rodan's nest being protected by the pterodon. Godzilla appears, interested in the egg, and the two fight over it. However, a Japanese team manage to sneak out with the egg as Godzilla defeats Rodan. Godzilla started making his way to Japan (once again) in search for the egg.
When Baby hatches from the egg, the team start researching the child and discover a second brain located in his tail, giving the military an idea that Godzilla has a second brain as well. They also discover that the baby is able to telepathically communicate with both Godzilla and Rodan, sending them closer towards the baby. Under the care of Azusa Gojo and Miki Saegusa, Baby is left scared since he doesn't know either Rodan or Godzilla.
In the climatic battle with Super Mechagodzilla, both Godzilla and Rodan are overpowered by the mech. Hearing the baby's cry, Rodan lands on Godzilla and re-energizes Godzilla's second brain in the cost of his life, allowing Godzilla to regain his strength and destroy the robot. When Godzilla locates Baby, at first Baby was afraid of the giant monster, until Miki uses her psychotic ability to calm Baby and convinces Godzilla to adopt the child. Baby Godzilla and his new father swim off to sea to find a new home.
Godzilla vs. SpaceGodzilla
A year has passed since Godzilla adopted Baby Godzilla. Now living on Birth Island, Baby Godzilla now is considered Little Godzilla, or Little One, as he grew about 30 meters. Little One first appears discovered by a Japanese crew, including Saegusa, to place a mind device on Godzilla, a test to prevent human casualties. Little One and Miki share a short reunion, until SpaceGodzilla, a fission between Godzilla's cells carried by Mothra and a black hole, arrives in front of Little Godzilla. Curious, Little Godzilla walks towards SpaceGodzilla, only to be captured. Godzilla arrives and tries to save his son, but to no avail. SpaceGodzilla imprisons Little One in his crystal fortress made out of the city of Fukuoka. Only after Godzilla and M.O.G.U.E.R.A. were able to defeat SpaceGodzilla in Fukuoka did the little monster walk free from his crystal prison and return to Birth Island with his father.
Godzilla vs. Destoroyah
After Birth Island's destruction after Godzilla's radiation begins melting down does Little Godzilla turn into Godzilla Junior, now resembling his father. Junior begins to search for his father by moving towards his birth island. The Japanese plan to use Junior as a lure to destroy Godzilla using the Oxygen Destroyer that killed the first Godzilla, to prevent him from exploding at taking the Earth with him. To do this, they conscript the two psychics Meru Osawa and Miki Saegusa to lure Junior to Tokyo, and hope Godzilla will follow. Junior is successfully lured to Destoroyah's position and attacks the giant crab-like creature with all he has. However, the young monster is knocked aside by Destoroyah and pinned down under the beast. Destoroyah then sinks it's mandibles into Junior's chest and injects micro-oxygen into the deep wound. Junior, however, finds the strength to retaliate and blasts Destoroyah away with his atomic ray at point-blank range. The Precambrian creature degenerates and breaks down as it falls, defeated, into an oil refinery. The refinery explodes, and Junior roars in victory. That night, Godzilla finally arrives and greets his adopted son on the outskirts of Tokyo.
Suddenly, Destoroyah rises from the burning refinery in its final, demonic form. The mutant beast takes flight and knocks Godzilla down. The monster then grabs Junior, dropping him in a building, and blasts him with his micro-oxygen beam, killing the young monster. Saegusa and Godzilla were very heartbroken for the death of Godzilla Junior, as they both knew another kaiju will die: Godzilla. With aid from the military, Godzilla succeeds in finally killing Destoroyah and then melts down. Radiation filled to skies of Japan turning it into a ghost city, but the radiation is absorbed when Junior rises, all grown-up and fully developed into an adult Godzilla, showing that Godzilla's legacy will never end.
- When fans look at Godzilla Junior as a young Adult in Godzilla vs. Destoroyah, he bear's a striking resemblance to Godzillasaurus.
- When Junior is revealed to have been reborn, the suit used for him is the one used for his father, only with the light bulbs turned off.