Giestron is the incarnation of the Earth's anger, emerging from the depths of the Earth to take revenge against humanity for polluting the planet. Giestron was sealed away by Takkong many years ago, but had returned due to Takkong's age taking a toll on its ability to seal Giestron away. Giestron emerged in the modern day from underground, destroying helicopters and buildings to take revenge on humans that have been polluting the Earth.
Takkong was still sleeping when Giestron appeared, being woken up by Shinji. The two monsters proceeded to fight each other, but Takkong was overwhelmed and beaten. Giestron then began to control the Earth's electromagnetic energy, trying to cause much of the planet's magma to seep to the surface and end the world. Taiga appeared and used his Hand Beam to interrupt the monster, engaging it in a fight. In his normal form, he barely did anything and got pushed away like Takkong. Giestron tried to attack him with an energy boomerang which was then blocked by Takkong. Taiga checked to see if the monster was okay before changing into Tri-Strium. The guardians of humanity then teamed up against the beast, both assaulting Giestron from different directions. Takkong spun around rapidly and surrounded itself in fire before ramming into the monster, dealing serious damage and allowing Taiga to come in with the Taiga Blast Attack, destroying Giestron and likely ending its threat for a long time to come. Taiga and Takkong then gave each other a high-five as celebration.
Before leaving, Shinji told Hiroyuki Kudo that Giestron may return someday if humans are not willing to change their ways.
- Designer: Daisuke Inomoto
- Like Kamisori Demaaga and King Galactron before it, Giestron first appeared in the year's Ultraman Festival stage show before making its way into the TV series.
- Interestingly, their mouths are often static due to the lack of a movement mechanism.
- Due to the use of Return of Ultraman's BGM and appearing with Takkong in its debut episode, its implied that Giestron is either a variation of Arstron or simply a monster that shared its body build.
- The Ultraman Taiga Super Complete Works magazine and Blu-ray Box II only stated that Giestron was designed under Arstron's inspiration. Additionally, its creation was also under demand by Takanori Tsujimoto.
- Its rivalry with Takkong and representation of the Earth is based on the rivalry of Ultraman Gaia and Agul in their season.
When Haruki Natsukawa was still in his elementary school years, Giestron attacked for some reason. His father went off to help other people, but never came back and lost his life in the process, leaving Haruki's mother to raise the boy by herself. The incident haunts Haruki to this day.
- Height: 60 m
- Weight: 25,000 t
- Origin: Underground
- Powers and Weapons
- Burrowing: Despite its need to create a hole in the surface, Giestron at the very least capable of carrying itself out from the depths of the earth.
- Body Spikes: Giestron has spikes all over its body, which it uses as weapons in combat. They are capable of manipulating electromagnetic energy for use in energy-based attacks.
- Giestron Lightning Wave (ギーストロン雷電波 Gīsutoron Raiden-ha): Giestron fires a thin yet highly concentrated beam of energy from its cranial horn.
- Giestron Giant Quake (ギーストロン大振波 Gīsutoron Dai Shin-pa): Giestron creates a storm by manipulating electromagnetic energy. It is able to cause the magma underneath the ground to emerge on the surface.
- Giestron Super Lightning Wave (ギーストロン超雷電波 Gīsutoron Chō Raiden-ha): Giestron forms an energy cutter between its arm blades before flinging it towards a target.