Gamera 3: Revenge of Iris (1999)

Three years have passed since Gamera defeated Legion and the world is once again plagued by Gyaos, which have now evolved into Hyper Gyaos. Mayumi Nagamine, noted ornithologist, returns to aid the Japanese government in addressing this threat. A graveyard of Gamera fossils is found at the bottom of the sea. Shadowy government agents, occultist Miss Asakura and Kurata Shinya, are meanwhile working with a different agenda, with Asakura believing Gamera to be an evil spirit.

A pair of Gyaos glide across Tokyo's Shibuya district, but are destroyed by Gamera at the cost of 20,000 human lives, causing the Japanese government to order Gamera's immediate destruction. Meanwhile, a young girl named Ayana, whose parents were inadvertently killed by Gamera during his previous battle with Gyaos in 1995, discovers a stone egg sealed within her village temple. The egg hatches a small tentacled creature, whom the girl names "Iris" after her dead pet cat. Iris forms a link with Ayana through an orichalcum pendant and becomes the focus of Ayana's quest for revenge as she seeks to raise her own monster and take vengeance against Gamera. Iris, however, attempts to absorb Ayana in the process of his growth. The girl's classmate manages to free her from Iris' cocoon, but it leaves its lair and kills half of the village's populace, subsequently growing into its adult form. The military attempts to destroy it, but fails.

Iris flies toward the city of Kyoto, where Ayana has been taken by Asakura and Kurata, with Asakura deliberately trying to use the girl to summon Iris. Iris is intercepted in mid-flight by Gamera and the two engage in an aerial battle, but the Japanese army intervenes and knocks Gamera out of the sky with a tactical missile strike. Nagamine and Asagi, the girl once psychically linked with Gamera, retrieve Ayana and attempt unsuccessfully to get her out of Kyoto. Kurata speculates that Gamera was engineered as Humanity's guardian, and as such is a "vessel" capable of being charged with humanity's collective "mana", and expresses a belief that therefore Iris had been deliberately created to defeat Gamera so the Gayos (acting akin a planetary immune systen) could wipe out the human race. Although they don't share Kurata's misanthropy, Nagamine and Asagi think that the mana theory explains from where Gamera got the energy he used to defeat Legion.

The two monsters meet and continue their fight, but Iris easily gains the upper hand, impaling Gamera and leaving him for dead. Iris then makes its way to the train station and absorbs Ayana, killing Asakura and Kurata in the process. From within Iris' body, Ayana experiences the creature's memories and realizes that her hatred and bitterness have motivated it. Just as she has her epiphany, Gamera plunges his hand deep into Iris' chest and wrenches the girl free, robbing Iris of its human merge. Miss Nagamine and Asagi, trapped within the train station's wreckage, watch helplessly as Iris impales Gamera's hand and begins to syphon his blood, creating fireballs with its tentacles. Gamera blasts off his injured hand and absorbs Iris's fireballs, forming a fiery plasma fist, which he drives into Iris' wounded chest.

Iris explodes, blowing the roof off the crumbling train station. The comatose Ayana still clutched in his fist, Gamera sets the girl down where Nagamine and Asagi are hiding. The women are unable to revive her, but Gamera lets out a roar and Ayana awakens. Gamera leaves the girl wondering why he would save her life after all that she had done. A swarm of Gyaos, thousands strong, begins to descend on Japan intent on destroying their greatest foe once and for all. Military leaders finally realize that Gamera is on the side of humanity and pledge to fight the Gyaos horde alongside him. Asagi says that, although she doesn't share a psychic link with Gamera anymore, she knows he will not back down and will fight 'til the end. As the swarm approaches, Gamera lets out a final roar of defiance as he stands his ground in the center of a blazing city.