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 triggered a reaction from its corpse. Overjoyed at the possible revival of her dear friend, Milim's hopes were quickly dashed. Because its spiritual and astral bodies were severely damaged, the hatred of the girl tainted the dragon's core, resulting in 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. Following that, it was then sent to eliminate Demon Lord Rimuru. Milim who was accompanying him in their exploration of the ancient ruins of Soma, was shocked at the appearance of the dragon who should've been sealed and engaged it once more to prevent its rampage. After a few events, the Chaos Dragon's spiritual and astral bodies were destroyed by her, and its core devoured by Rimuru. In a show of generosity to Milim, Rimuru collected its damaged core and placed it in a pseudo-soul. Once the soul successfully housed the core, Rimuru followed it up by encasing them both with a master core, creating an avatar core which is akin to an egg. After the dragon's damaged core finished healing, the egg hatched marking the rebirth of Milim's dear friend.

Relationships
Milim Nava: His friend and master. After his rebirth, the two have gotten very close and are always having fun, at the cost of Milim receiving a harsh scolding from Frey. His 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
Having been blessed with the Earth spirit, Gaia has the ability to manipulate gravity.

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

Gravity Barrier: dulls physical attacks.