The Devonians are a race of aquatic aliens that lived under Terra's oceans after their original home planet was destroyed during the Thousand Years War. They had a hatred for the humans because of their habits of polluting the oceans. They had a shaky alliance with he Cryogs until the Devonian King betrayed them which resulted in the Cryog leader Commander Rhizon in giving the locations to the humans and leading to the destruction of the entire Devonian capital.
In appearance, the Devonians appear to have a hominid body structure and are about the size of a normal human, having muscular arms and legs. Their skin is scaly and green. They have three clawed toes and three clawed fingers. They have orange eyes and have sharp teeth in their mouths. One either side of their heads are large fins and on the top of their heads are a fin like structure. On their chins are two small protrusions that point inward.
The Devonians are a race of aquatic fish-like humanoid aliens that lived on their ocean planet thousands of years ago. They got caught up in the Thousand Years War between other alien races and the Devonians allied themselves with the Xillians and the Nebulans. As a result, the Kilaaks soon invaded the Devonians home world with their Kaiju Hedorah, the Devonians contacted the Xillians for help and their war ally sent Monster X to deal with the Smog Monster. Unfortunately the battle became to chaotic, it resulted in the destruction of Devonian home world. The survivors travelled across space in search of a new home and they soon came across Terra (commonly known as Earth) and settled on there, living in the oceans.
After the events of King Caesar and Megalon's battle and a Cryog ship crashed (which had been shot down by a Millennian UFO) into the ocean, the Devonians found the ship and the pods of containing the Cryog crew. Over time as humans began to advance over the years, the Devonians grew to hate them for polluting the ocean and intruding into their domain, they wished to destroy them as well as wanting to destroy Godzilla as they saw him as a threat.
In 2010, the Devonians managed to the Cryog again this time lead by Commander Rhizon and the two races managed to form an alliance to wipe out the human race and rule Terra. While the Cryogs go to a CKR to recover a sample of Godzilla DNA, the Devonians managed to take control of Destoroyah and send her to attack San Diego in her juvenile forms. The Devonians also manage to take control of Manda and Gezora, sending the two sea monsters to attack the USS Goldstein. The Cryog soon send the Godzilla DNA sample to the Devonians to create a new weapon and they soon send Destoroyah to attack Godzilla until Mothra, Mothra Lea and Baby Mothra come to Godzilla's aid.
While the Cryogs retrieve the still living remains of Orga, the Devonians give the coordinates their location to the aliens so they can meet. After the Cryogs' ship is damaged by Jet Jaguar, the ship arrives at what would become Monster Islands and Commander Rhizon confronts the Devonian King. The Devonian King breaks the truce between the two races as he states the Cryogs believe that the Devonians are primitive and won't tolerate the Cryogs ruling Terra. With the Cryogs' ship damaged, the Devonians unleashed their newest creation onto the Cryog ship: Biollante. With several human ships heading towards their location, the Devonians unleashed Manda Gezora and now Titanosaurus who they have now under their control until they are driven off by Godzilla.
While Lucy Caprell is on Infant Island and is shown the history of the kaiju by the Shobijin, the Devonians appear in a flash-back where they are at the sunken Cryog ship, inspecting it and observing the stasis pods of the Cryog crew.
After Commander Rhizon survives Biollante's attack and disguises as a Devonian rebel, he tells the humans the existence about the Devonians as he intends to have the humans destroy the Devonians as revenge. Meanwhile while the CKR are tracking Godzilla's location at sea, the Devonians sense Godzilla near the surface and they unleash Destroyah, Titanosaurus, Manda and Gezora against the King of the Monsters. The Devonian King becomes aware of the humans plans for creating the Monster Islands facility. After a sonar beam sends Titanosaurus, Gezora and Manda into retreat and Godzilla grabs onto Titanosaurus as he follows the three, the Devonians sends Destoroyah to destroy the humans while they deal with Godzilla.
They sense Gezora getting blasted onto the ceiling of their base. Soon Godzilla, Titanosaurus and Manda crash through base as they battle, several Devonians are killed in the kaiju battle. Some of the survives go to their ships but the ships are destroyed and so they try to go to a Cryog ship in their possession. As Titanosaurus and Manda retreat, several missiles are launched by human submarines as they target the Devonian capital. As the missiles strike, the Devonians are destroyed and Godzilla is buried under a rock slide.
Tenrou Island Arc
While the Devonians themselves don't appear, they are seen in the memories of Manda. In 2016, the Earth Defenders and the Earth Conquerors are transported to Earth Land, and the Earth Defenders join Fairy Tail and the Earth Conquerors join Grimoire Heart. On Tenrou Island, during the battle of Erza Scarlet, Juvia Lockser and Manda face Meredy and Gezora, Manda explains to her Fairy Tail allies her connection with Gezora and how they served the Devonians. As Gezora attempts to choke Manda, Juvia is able to see into Manda's memories (being connected through Meredy's Sensory Link) and she see's the Devonians attacking Manda in the memories.
Aquatic Life-Style: Being an underwater species, the Devonians are adapted swimmers.
Advanced Technology: The Devonians were able to posses advanced technology after they found the crashed Cryog ship thousand of years ago. With technology they were capable of genetic emerging and able to create Biollante and are also able to mind control kaiju.