Encounter and Vow (出会いと誓い) is a special story included in the DanMachi BD Volume 6 booklet.
In the Elven forest that she lived in, Ryuu was the member of a family that cared for the sacred tree. Because of this, ever since she was born, she received combat training. Even if they didn't have the falna, they were still capable of driving off monsters on the surface using swords or bow and arrows.
One day, Ryuu and her fellow family members drove off a group of merchants from entering their forest. Once they returned home, the adults mocked them, calling them dirty and ugly. As time passed, she began to think that beautiful Elves were the ugliest of all people. No matter how much she tried to forget it, once she began thinking about it, the thought firmly planted itself in her mind. Eventually, Ryuu decided to leave the Elven forest, taking with her some Seiros ore to have some money on hand.
Once she left the forest, she made her way to Orario, thinking that she could make friends where every race mingled together. However, even there she continued to reject people. She could've tried to get help from other Elves but her thoughts prevented her from doing so. Ryuu began wearing clothes that covered her whole body along with a mask. As time passed, she began to believe that she was looking down on others just like the others in her home forest because of how she was rejecting them.
While she stood alone in an alley in the rain, a voice called out to her from behind. Turning around, she knew that the person was a Goddess. Ryuu was apprehensive of Gods, as when she first came to Orario a certain Goddess and others exhibited behavior that made her appalled. When Astraea mentioned that she looked lost, Ryuu's anger exploded, blaming the Gods for creating Elves. Astraea accepted her anger without saying anything. After listening to her, she told Ryuu that what she needed was a friend that she could see as an equal, not a God. Astraea handed her a map to her home along with some food and left.
Ryuu began to think that the liveliness in Orario lacked something definite. The public order within Orario was somewhat lacking, with fights and problems occurring across the city. One day, Jura and his group surrounded Ryuu in an alley, knowing that she wasn't connected to any God. They planned to sell her off to a brothel though their plans were ruined by the arrival of Alise who quickly sent them running. Alise managed to convince Ryuu to trust her and took her to her Familia's home.
Alise led Ryuu to the Astraea Familia home. While there, Alise explained that the Astraea Familia was not only an exploration type Familia but also acted to keep order within Orario. The Freya Familia, Loki Familia, Ganesha Familia, and the Hephaestus Familia were still growing, though she declared that they would rise to help end all of these problems. As the others watched, Alise told Ryuu that they needed companions to help achieve this goal and asked Ryuu if she would join them. Ryuu agreed to join the Astraea Familia and was given the falna.