Species Mutant Gyaos
Form(s) Baby Form and Adult Form
Height 99 metres
Tentacle Length 1,999 metres
Weight 199,000 tons
Air speed Mach 9
Irys (sometimes spelt Iris in the East) is the antagonist Kaiju from the third film in the Heisei Gamera trilogy, "Gamera 3: Revenge of Irys". Its physical appearance harkens back to the tentacled entities of the Cthulhu Mythos. Irys is Gamera last arguably most powerful opponent faced (many fans view Legion as Gamera's strongest enemy).
Form and abilities
The baby Iris has an armored, mouth-less head with small black eyes, and several long tentacles which sprout from a snail-like shell. It can 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 realised on-screen by a remotely-operated puppet.
The adult Iris is basically a bipedal creature with two hooved legs and retractable sword-like arms, 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 hundreds 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, bioluminescent patches. The center patch can suck things into its body.
editHistory within the film
Iris begins its life as a stone egg, sealed within a small underground temple in Nara village and guarded over by a family line named Moribe - local legend said it was the resting place of a demon called Ryu-Sei-Cho. (A character explains this name to be linked to Chinese mythology) A stone of unknown origin is said to keep the demon dormant as long as it's not moved.
A young girl named Ayana Hirasaka - left an orphan by the 1995 Gamera/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 & an amulet, similar to the one that linked Asagi to Gamera in the first film. The egg later hatched, produced an infant Iris.
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 it 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 kaiju-sized in the woods as it devours several villagers, including Ayana's adoptive parents and brother. Shortly, the monster grows into its adult form.
The Japanese Self Defense Force quickly deploys and surrounds Iris as it sleeps, attempting to take it out with machine guns and bazookas. 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 to kill it. 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' armor 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 and ending its reign of terror.
origins and motives
The origins of Iris are not explained, and instead the film presents Chinese mythology as explained by Ayana's adoptive brother, the beliefs of the Moribe clan matriach, the theories of government agent/misanthropic recluse Kurata Shinji and the actions of government agent & cultist Ms Asukara.
Grandmother Moribe states that the Ryu-Sei-Cho is a demonic creature that will destroy the world if it is ever released. In contrast, the mythology that the Ryu-Sei-Cho name comes from suggests that the being is the mythical "Guardian of the South", who will defend against a threat from the South; a tortoise (hinted to be Gamera) is said to be Guardian of the North and Ayana asks if the two Guardians are rivals (this was unconfirmed). 
Asukara, who (at the start of the Kyoto battle) Kurata refers to as a former shrine priestess and hints her bloodline goes back to the Atlanteans, believes Iris to be a savior against the "evil spirit" Gamera who threatens to destroy Heaven and Earth. With Kurata's help, she has Ayana moved from hospital to Kyoto, where she's built a shrine and where she attempts to use Ayana & her amulet to deliberately draw Iris to Kyoto. She later seizes the amulet for herself to join with Iris against Gamera (calling it "the God Naibo") and the amulet does appear to react, but no serious connection is made and she's killed in the process.
Kurata's belief is that Iris was designed by "the ancients" (Atlanteans), as Gamera and Gyaos was, but with the specific intention to stop Gamera from saving humanity from the Gyaos - "there could be a worse future for Earth than our extinction" and Iris was created to stop that future. He theories it will permanently merge with Ayana to gain power, similar to how Gamera bonded with Asagi but to a greater degree so it can overpower the guardian. Here, Iris is basically out to ensure extinction of mankind (something he openly likes the sound of).
Kurata's belief fits in with what is shown of Iris and its actions: it is specifically awoken by the Gamera-hating Ayana, who lifts a stone it is stated a sumo wrestler couldn't move; like Gamera, it has an Atlantean amulet that links it to a human (effectively making it the anti-Gamera); through Asukara, said to be an Atlantean descendant, it is shown there is a long-running religious belief that Iris will protect Earth from destruction by Gamera; and after it is destroyed and Gamera is wounded, Gyaos flock towards Japan as if they know it's left them an opening.
It is also shown that Ayana's hatred and malice drives Iris, and it was her influence that caused it to massacre her village & adoptive family and seemingly her influence that causes it to attack Gamera. This could mean Iris' development was warped by contact with Ayana and it would not have been hostile otherwise, or simply that the creature was designed to be awoken by and to seek out individuals with such hostility in them. However this is opean to interpation.