You cannot separate the world into 'people' and 'monsters.' Taking a life in battle may have meaning, but this is murder.
Ayda was born into a family of Guardians who had protected the forests in Greenhill Principality from poachers for generations. Ayda grew up to be such a Guardian herself, in her father's image, making full use of her knowledge of the forests and her skills as an archer.
The scar on her left cheek comes from a fight with some of these poachers and she considered it a badge of honor. At some point, Ayda's parents were killed by griffins although she bore the creatures no ill-will over the incident.
Perhaps because she was raised around animals and nature since birth, Ayda had a special ability to connect with animals and other creatures through their hearts. As she was unused to socializing with people, she could sometimes come off as unfriendly but in truth, Ayda was a very kind-hearted woman who truly loved the natural world.
Early in the Dunan Unification War, she would have an encounter with Nash Latkje when he inadvertently bought a horse belonging to Ayda from Hoi, who had stolen it. The misunderstanding would be soon cleared up and Ayda would take her ire out on Hoi, driving him from the forest.
Later during the war, an injured griffin arrived in the Forest Village and Ayda tried to stop the villagers from killing it. She stated that if the griffin were to recover and attack, she would fight it, but to do so when he was injured would be murder and would hold no meaning. When a group of griffins swooped in to attack Feather, Ayda tried to defend it but was defeated. The hero and his companions then arrived to help her.
After the incident, Ayda decided to join the New State Army, feeling the root of evil would be more swiftly severed at its source and that the Highland Army present an existential threat to the forests.
Ayda liked the New State Army Headquarters although she did miss the forests she was accustomed to. She also formed a bond with Kinnison, due to their similar backgrounds, and he may have had a crush on the young Guardian. She served as an archer captain during the war and her ability to navigate forests proved helpful to any unit she was part of.
Following the Dunan Unification War, she returned to the forests in Greenhill to live in harmony in nature and protect it. Her maxim was that she was born in the forest, her life is dedicated to protecting the forest, and she says she'll die in the forest. Even after the war she was occasionally visited by Kinnison.
Once your castle is at Level 3 or higher and if you have at least one set of Listening Orbs acquired from recruiting Badeaux, go to the Forest Village and meet Ayda then use the Listening Orb when prompted.