Eimer serves as the pilot of the Glass Battleship and is widely regarded as one of the most skilled pilots, capable of maneuvering the vessel with great speed and precision. She possesses a brash and energetic personality, often speaking in a rough manner that contrasts sharply with her cute appearance, and as a result, her crewmates rarely treat her like a typical girl. She has brown hair usually styled into twintails, red eyes, and is known to wear boots and gloves. In combat situations, she is resourceful and fights with knives when necessary.

Before joining Cleo's crew, Eimer lived in a small village where she was the leader of her community. However, an attempt to protect her village ended in disaster, causing greater harm than good, and she was subsequently betrayed by those she tried to save. This event drove her from her home and led her down a path of revenge against the lord responsible for her village's ruin. During her failed assassination attempt on the lord, she met Cleo, who quietly observed her actions. Though she only managed to breach the gates, a power outage at the lord's mansion spared her life, and Cleo successfully stole an energy source needed for his ship, using her attack as a distraction. After this incident, Cleo invited her to join his crew, and she has remained a loyal member ever since.

Within the crew, Eimer has a well-known secret crush on Cleo, and she exhibits great enthusiasm whenever he is involved, willingly placing herself in danger to protect him. She shares a notable dynamic with her fellow crew member Nowy, whom she constantly teases; the soft-spoken and somewhat dorky Nowy often drops his glasses, sometimes intentionally, in an effort to make her laugh. This contrast establishes a classic red oni, blue oni pairing between the bratty, arrogant Eimer and the gentler Nowy. Early in the story, before discovering the truth, she developed a significant crush on Michel Volban, the leader of the People's Army. This infatuation led to a pivotal incident where she attempted to spy on Michel while bathing, and her subsequent fall through the roof accidentally exposed Michel's true gender as female to the entire crew. Despite her tough exterior, she is not evil, and her red eyes serve as a subversion of the typical warning sign of a dangerous character.

Her development is explored in depth, including a dedicated flashback episode late in the series that details her time as the "Queen of the Slums" and her first encounter with Cleo. This episode provides further insight into her brash nature and how earlier life events shaped her personality. Her motivations are driven by a deep sense of loyalty to Cleo, who saved her life and gave her a new purpose after her village betrayal. Her role in the story is that of a capable and enthusiastic action girl whose piloting abilities are essential to the Glass Battleship's operations, and whose personal entanglements with both Cleo and Michel drive key relationship dynamics and plot revelations within the crew.