Iris shares its name with a goddess from Greek mythology, and also a type of flower. In-universe, Iris gets its name when Ayana Hirasaka names it after her dead cat. An alternate spelling of Iris' name is Irys. This is another possible translation from Iris' Japanese name, but has never been used officially, aside from some early Japanese advertisements and merchandise released around the film's release. In the West, the use of the name "Irys" has been popularized by fansites, despite the name "Iris" being used in all official western releases of Gamera 3.
The baby Iris has an armored, mouth-less head with small black eyes, and several long tentacles which sprout from a snail-like shell. Although Baby Iris lacks a mouth, it can consume and absorb the life force of organic matter by stabbing them with its tentacle spears, leaving decayed corpses in its wake. The Behind-The-Scenes feature on ADV Film's DVD shows it was realized on-screen by a remotely-operated puppet.
The adult Iris is basically a bipedal creature with two hooved legs and retractable sword-like arms (also known as Machine Hands), topped by a head that resembles a pointed seashell. Its back is a mass of saw-edged plates, and from its sides spring four tentacles thousands of meters long. Each of these is tipped with a bony spearhead, from which Iris can fire a sonic beam similar to the Gyaos. Iris can still drain the life force from its victims, and in the case of Gamera it was able to absorb the monster's abilities and produce its own fireballs. Its chest region is also covered in glossy, bio-luminescent patches. The center patch can suck things into its body.
As an infant, Iris is extremely docile and affectionate towards Ayana Hirasaka, allowing her to raise it like a pet. As Iris grows, it becomes more aggressive, actively killing small animals and later countless human beings in order to feed on their life force, though it remains loyal and harmless towards Ayana. It is revealed that Iris wiped out a large portion of Ayana's village, including her adoptive family and the various people who antagonized and tormented Ayana. When Ayana refuses to allow Iris to merge with her after it attacks her friend Tatsunori Moribe, Iris forcibly absorbs her into its chest, showing her visions of it killing her adoptive family. Whether Iris was born as a malevolent entity and was simply using Ayana to increase its own power or if it was created as a benevolent guardian and corrupted and twisted by Ayana's hatred is never revealed, so the creature's true intentions are unknown.
Iris does not have a definitive origin, though multiple theories are put forth in the film. According to the legends of Nara, Japan, Iris is an ancient demon known as the Ryuseicho that, if awakened, will bring about the end of the world. Other East-Asian mythologies suggest that Iris is the Guardian of the South, represented as a giant bird, which battles against an enemy guardian from the north, represented as a giant turtle. Kurata Shinya, a computer programmer who studied Gamera, Gyaos, and the Atlanteans closely, proposes that Iris may have been created as a failsafe measure by the Atlanteans for the sole purpose of killing Gamera if he ever became too powerful or no longer served the planet's best interest. Analysis of Iris' DNA showed it to be genetically identical to the Gyaos, only with the ability to alter its own DNA, leading to the theory that it is either a mutation of or the ultimate evolution of the Gyaos. Iris' genetic connection to Gyaos and the presence of black Atlantean beads in its shrine that telepathically link Ayana to it (a dark reflection of Gamera's bond with Asagi Kusanagi) confirm that Iris has some kind of connection to the Atlanteans and is related to the Gyaos, however the exact specifics of what Iris is and why it was created are never definitively said.
A young girl named Ayana Hirasaka, left an orphan by the 1995 Gamera and Gyaos battle and blaming Gamera for her parent's deaths, entered the cave on a dare and moved the stone. In the process she and the latest son of the Mirobe line discover both the egg and an amulet, similar to the one that linked Asagi to Gamera in the first film. The egg later hatched into Baby Iris (ベビー·イリス?). Bebī Irisu
Ayana gains a link to the creature via the amulet and feels a kinship with the creature, stating at one point "Gamera killed its family too"; driven by total hatred for Gamera, she raises Iris, naming it after her dead pet cat, in hopes that it will become strong enough to kill him for her. It was shown to have an affectionate nature, but this is shown alongside the sinister way it eats and, later in the film, the woodland animals it leaves dead.
It is not long before Iris attempts to merge with Ayana, and her actions show she's willingly letting it do so, by sealing her in a cocoon. Moribe discovers her and cuts her free. She is then taken to a hospital. While Ayana is gone, Iris grows into a giant monster in the woods as it devours several villagers, including Ayana's adoptive parents and brother. Shortly, the monster grows into its adult form.
The J.S.D.F. quickly deploys and surrounds Iris as it sleeps, attempting to take it out with machine guns and bazookas. The weaponry only seems to irritate the creature. Some of the soldiers are killed before Iris takes to the sky and heads for Kyoto, where Ayana had been transferred earlier. The JSDF sends two F-15s in an attempt to shoot Iris down, but it is able to evade them and almost kills them. The fighter pilots are saved by the sudden arrival of Gamera, who engages Iris in a mid-air battle. The JSDF ends the battle by shooting at Gamera, which slows him down and allows Iris to continue on to Kyoto.
Soon, Iris lands in Kyoto and fights Gamera on land with Ayana watching and commanding it to kill him. Iris manages to knock Gamera down for the count and then attempts again to merge with Ayana; when Moribe intervenes, the creature swats him aside and sucks her into its body against her will. While inside, Ayana realizes that she fueled Iris' destruction with her emotions - it was her hatred that led to the death of her adopted parents, and Super Gyaos instead of Gamera actually killed her parents. All seems lost until Gamera suddenly punches through Iris' chest and rips Ayana out.
Infuriated, Iris pins Gamera's hand to a wall with its spear hand and begins to absorb Gamera's energy. Its tentacles begin to form plasma balls, when Gamera quickly uses a plasma ball himself to sever his own hand. Iris fires the absorbed plasma balls at Gamera who uses his stump to turn the plasma into a plasma fist. Gamera then uses the fist to slice through Iris' chest, killing it.
- Iris has a hard carapace similar to a turtle shell.
- Like Gamera, Iris has his own bead with which he can communicate with Ayana, strengthening him.
- Iris has four tentacles which can be used to absorb nutrients from other organisms. They were also used to deflect Gamera's fireballs.
- Each of Iris' tentacles is tipped by a bony arrow head shaped covering that can open. It can fire the same sonic beam as the Gyaos.
- Iris can open membranes between its tentacles which it can use as wings, allowing it to fly at Mach 9.
- Each of Iris' arms sport a retractable blade. The blades can pierce Gamera's body and absorb body fluids.
- Iris can analyze the DNA of any creature's body fluids it absorbs via its arm blades.
- Like the Gyaos, Iris can manipulate its own chromosomes to adapt and evolve to suit its environments. It can also adapt to incorporate and DNA it absorbed.
- The same technique used by the Gyaos, Iris can fire the Sonic Scalpel beam from any one of its Tentacles via their bony tips.
- After it had absorbed Gamera's DNA, Iris could then fire Fake Plasma from its tentacle tips.
- Main article: Iris/Gallery.
- Although Mother Legion is the tallest opponent Gamera has faced, Iris is easily the longest, with his adult form's tentacles being nearly 2 kilometers long when fully outstretched.
- Like SpaceGodzilla, Iris' origin is contested. While it is assumed that like Gamera and the Gyaos, Iris was created by the Atlanteans, it is also suggested that Iris is the Guardian of the South in East-Asian Mythology, corresponding to the real Vermilion Bird constellation. All that is known is that Iris is genetically related to the Gyaos, and has some kind of connection to the Atlanteans. Whether they in fact created Iris and why they did is unknown.
- Iris is the sole monster in the series who has no mouth. However, this doesn't hinder its communicative abilities. As a baby, Iris makes light chirping noises, while as an adult, it makes loud droning and humming sounds.