Gaia

Gaia (ガイア), formerly known as the Chaos Dragon (沌竜とし), is the pet dragon given to Milim by Veldanava.

Background
Veldanava used up the last of his energy to gift his daughter a pet dragon, in the hopes that it would one day serve as a vessel for his soul. After he and Lucia passed away, the pet dragon became Milim's only family; it lived peacefully with the dragon princess for an unspecified amount of time before becoming the target of a certain kingdom. The foolish kingdom incurred the wrath of the dragon princess for taking the life of her friend and as a result, was destroyed. After Milim awakened as a True Demon Lord, her connection to the pet dragon caused the dragon to revive. But because its spiritual and astral bodies were severely damaged, it revived in a corrupt state, becoming an abomination that transcended both good and evil. Milim, in her sadness, sealed her former friend away to end its destruction.

Majin Behind the Scenes arc
The corrupted dragon was unsealed by Free Guild Grandmaster Yuuki Kagurazaka after discovering its location through the Guild's network. It was placed under Mariabell Rosso's control and further corrupted under the influence of her Unique Skill Greed. It was then sent to eliminate Demon Lord Rimuru. Milim who accompanied him in their exploration of the ancient ruins of Amrita, was shocked at the unexpected appearance of the dragon, and engaged it once more to prevent its rampage. Overpowering it, Milim destroyed the dragon's spiritual and astral bodies, and its core was devoured by Rimuru. In a show of generosity to Milim, Rimuru fixed its broken core and revived it with a psuedo soul.

Relationships
Milim Nava: It's friend and master. After it's rebirth, the two have rekindled their once intimate relationship, and often fool around, at the cost of Milim receiving a harsh scolding from Frey. They're each other's playmate when exploring the labyrinth.

Rimuru Tempest: They're friendly with each other. His playmate when exploring the labyrinth.

Veldora Tempest: They're friendly with each other. His playmate when exploring the labyrinth.

Ramiris: They're friendly with each other. His playmate when exploring the labyrinth.

Abilities
Holding a strong affinity with the earth attribute, Gaia has the ability to manipulate gravity.

Chaotic Breath: a highly concentrated miasma that corrodes anything it touches.

Gravity Barrier: dulls physical attacks.