Gaia

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 his passing, 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. This foolish act incurred the wrath of the dragon princess for taking the life of her friend and as a result, the kingdom was destroyed. When Milim awakened as a True Demon Lord, her connection to the pet dragon seemingly brought it back to life.

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. In her sadness Milim sealed her former friend away to end its destruction. However, the dragon's energy slowly seeped from its body and ruined the surrounding nature.

After an unexpected turn of events, its core was consumed by Rimuru, and through his generosity and efforts, was brought back to life. She currently lives with Milim within her domain.