Ermine

Edgar's former attendant. She is tall and a recognized beauty, but she always dresses as a man for ease of movement during combat. She is Raven's half-sister, but unlike him, her skin is fair.

She and Raven were sold as slaves to the Prince's organization, where she met Edgar. She soon developed feelings for him, but to torture Edgar, she was assaulted by the Prince right before his eyes, leaving deep emotional scars. A few years later, she escaped from the Prince's organization with Edgar and the others. Fearing she would become just another servant once he achieved his desired status as an earl, she sought to be a special presence in his life by remaining a fugitive with him. As part of a deal to buy some time, she acted as a spy for the Prince. However, with Lydia's help, Armin sensed they were getting closer to the seemingly unattainable treasure sword. She confessed her betrayal and, to sever the ties between Prince and Edgar, threw herself into the sea before witnessing Edgar obtain the sword.

Armin once lost her life but was revived by Ulysses as a selkie (seal fairy) and appeared before Lydia and the others. Despite being part of the group, she exhibited suspicious behavior secretly, and her actions indirectly influenced Edgar becoming a Prince. Due to her unclear intentions, she was in a delicate position. Later, it was revealed that her spy activities were under Francis's orders to ensure Edgar's survival. Lydia felt that since Armin entrusted her selkie pelt, the essence of her life, to Edgar, her soul would eternally belong to him wherever she might be. Even now, Armin often works alone to support Edgar and Lydia, frequently coming into contact with Kelpie, with whom she begins to share mutual trust as comrades with the same thoughts towards certain people.

Following orders from Ares, she joins Mermaids Rosa, who has come to London, and Mellow Jet, who came to inform them of anomalies in the fairy kingdom (Ulysses's corpse being possessed and moving around), on a journey to find Fire Agate, the counterpart to Bloodstone. Along the way, she hears stories from an old selkie who once took care of her and learns that the true owner of the "Heart of the Selkie" Lydia possesses might know the information they seek. Returning to London, she uses her selkie abilities to gather information from Lydia's aquamarine and joins the group to search the fairy realm beneath the Tower of London. They successfully find the Fire Agate but are trapped in the collapsing area triggered by a fire above ground. Though her heart was gradually becoming more fairy-like as she carried her pelt during the journey, she asked Kelpie, who accompanied her, to let her die as a human and entrusted him with her final wishes.

In the anime, she has already become a selkie at the start (therefore, the events involving her on Manann Island do not occur), and she is with Ulysses. Consequently, Lydia only knows Armin by name.