She is a beautiful woman who appeared to be in her twenties, according to human standards. Her skin was light with well defined facial features. She was stated to be semi-transparent.
Generally she wears a full length, aqua colored dress with white sleeves and goes barefoot.
Forest Disturbance Arc
She met one of Souei's clones during his investigation of the orc army and insisted that she meets Rimuru. She made her appearance in a meeting, where she confirmed the presence of an Orc Lord and asked Rimuru to defeat it.
Sometime later, she confronted Laplace and Gelmud and levied "divine justice" against them. She cut off one of Laplace's arms, but they escaped before she could finish them off, leaving her dissatisfied.
After the battle between Rimuru and the Orc Disaster, a conference was held to determine the fate of the orcs. Treyni attended the conference as a representative of the Treants. The Jura Forest Alliance was soon established, and she appointed Rimuru as their leader. Treyni and the Treants offered to provide a food supply for the orcs.
Demon Lord Attack Arc
She appeared with her sisters to witness the duel between Rimuru and Gazel Dwargo.
She later appeared during the battle against Charybdis and aided Rimuru's troops and the Pegasus Knights. After the battle, she questioned how Phobio discovered the location where Charybdis was sealed. The interrogation revealed the Moderate Harlequin Alliance as one of the factors responsible for the Orc Disaster and Charybdis incidents.
She was seen again answering some questions from Rimuru about Superior Spirits.
Human-Monster Interaction Arc
She appeared briefly to inform Rimuru about the arrival of the Eurazania's delegation and Youm and his group.
She can manipulate the magic power of nature. In particular, Dryads have the ability to transfer their consciousness to the trees and grass within the Forest of Jura. This allows her advanced informational gathering ability.
She has a teleportation skill, that looks like Spatial Travel.
She has the ability to unify her own strength with the spirits she summons. It is unknown if this is an extra skill or a form of magic.
Rimuru also made her a core to house her spirit similar to the Chaos core. Soon after Rimuru also makes her a body carved from the tree which served as her original body, giving her a unique, mobile body. Afterwards, Rimuru speculates her to be a sub demon lord in strength.
- Ramiris: She was always waiting for Ramiris to reincarnate. And was not aware of the fact that the Fairy Queen had become one of the Demon Lords, until being informed by Rimuru. She then became her subordinate.
- Veldora Tempest: Veldora once protected her in the past. She has felt a debt to him ever since.
- Rimuru Tempest: She holds great respect for Rimuru as she openly supports him as the leader of the new nation of The Jura Forest Alliance.
- Benimaru: Treyni and Benimaru seem to be on good friendly terms with each other and seem to get along.
- Shion: Treyni and Shion seem to be on good friendly terms with each other and seem to get along.
- Shuna: Treyni and Shuna seem to be on good friendly terms with each other and seem to get along.
- In The Slime Diaries, Treyni is shown to have a fondness for potatoes. She also said that Dryads are born from potatoes leading to the obvious joke that Treyni might be a cannibal due to her near constant consumption of potato chips.