Gamera 4: the Truth is a fan-made sequel to Gamera 3: Awakening of Irys. It's run time is about 45 minutes, and it has never been shown outside of Japan.
The story starts right where Gamera 3 ends, with the JSDF rushing to confront the swarm of Gyaos invading Japan. Squadron after squadron, jets dogfight with the Gyaoses, only to be mercilessly defeated by the monsters. A wounded Gamera takes off from the burning ruins of Kyoto to join the midair battle, where he spins off wild mana shots that pick off a few Gyaoses. Ganged upon by his malevolent opponents, Gamera's troubles are complicated when the swarm is joined by Albino Gyaos, a larger, souped-up, all-white version of the Hyper-Gyaos. Finally, all take aim and fire their super-sonic beams on Gamera, plunging him to a watery grave.
Following the battle, the Japanese government enlists the help of Nagamine and Osako to help the military search for the new monster. After locating it, the JSDF deploys a large force of tanks, rocket launchers and helicopters, but the A-Gyaos proves too strong for them. Later, the A-Gyaos attacks the hotel Osako is staying at, and he is presumed dead in the rubble. Finally, the military pits a heat ray tank, the SGPM-2, against Gyaos, but it, too, fails miserably.
One of the ancient Gamera skeletons is given mana power from the earth and regenerates into a new Gamera! Landing in Yokohama Bay, Gamera lays waste to everything in sight. A-Gyaos arrives to attack Gamera, and the two engage in a climactic clash. The new Gamera eventually prevails over his arch nemesis, yet does not return to the sea. Instead, he continues on a rampage, stomping and burning everything from Yokohama to Shinjuku. The JSDF launches a last ditch offensive in Shinjuku using heat ray tanks, but Gamera easily thwarts the attack. Suddenly, a huge explosion erupts from Gamera, and central Tokyo is reduced to smoldering ruins.
In the above sequences, the drama recedes into the background and what we get is about fifteen minutes of raw action. Again, considering the limited resources of the production, the effects are amazing. Whereas previous scenes were either completely CG or completely suitmation, those in the climatic sequence alternate between the two. Of course, no such transition is seamless, but at least the cuts are relatively smooth.
The battle techniques used by the monsters are very creative. Both A-Gyaos and Gamera come up with their share of original techniques. Gamera now uses plasma fireballs and a continuous flamethrower stream reminiscent of the original Gamera's breath. Gyaos is able to deflect blasts of this sort with a supersonic shield, which Gamera overcomes with plasma sabers from the tips of the largest claw on each of his arms. In essence, despite a budget with severe limits, these bits go far to show that the filmmakers' imagination had no limits.
No doubt some people are wondering why the new Gamera is so mean spirited. His acts of destruction near the end are extremely violent, as if powered by a deep hatred. But the last scene, a sort of epilogue, answers some questions and, in true Gamera style, raises more:
Soon after the climatic action sequence, we see Osako is still alive in Okinawa (as far away from Tokyo as possible), wondering how he always manages to survive such calamities. As he hobbles away, we hear a news broadcast. It turns out that the new Gamera opened a crater one km wide and four hundred meters deep in the center of Tokyo. The Japanese and US military found many unclassified prehistoric eggs deep within the crater. And so we are left to wonder if that was Gamera's real target. This is an interesting resolution that clearly leaves room for Hayashiya to continue his thread of the Gamera saga if he so chooses.