On the outside, Beatrice appears to be a lovely young girl around the age of eleven or twelve. Her face is so sweet that Subaru believed no heart could resist melting at the sight of her genuine smile. Her large sky-blue eyes feature pink butterfly patterns in their irises. Beatrice’s pale cream-blonde hair is long and styled into frilly, drill-shaped twin tails that bounce like springs when pulled. In the anime adaptation, the tips of her twin tails are dyed pink.

Most of the time, the Great Spirit of the Forbidden Library can be seen wearing a pink frilly ornate dress with white trimmings and an open front that leaves her legs visible, covered by pink and purple vertically striped tights. She wears a petite crown on the right side of her head, which complements her elegant appearance. Beatrice also has pink shoes with butterfly straps, a large pink ribbon on the left side of her waist, and similar ribbons tied at the top of her twin tails.

During her stay at the Water Plumage Inn in Arc 5, Beatrice wears a yukata.

Beatrice often comes across as haughty and condescending, looking down on others and struggling to connect with people who try to get close to her. She takes pride in her vast knowledge of yin magic and her identity as Echidna’s daughter, though this pride sometimes causes conflicts with others. Beneath her stubborn and teasing demeanor lies a softhearted and easily flustered girl who dislikes showing weakness. Her speech is also distinct, as she frequently ends her sentences with phrases like “I suppose” and “in fact.”

After the attack on the Sanctuary by Hector, Beatrice became deeply lonely. The loss of her closest friend Ryuzu, who sacrificed herself to protect others, left Beatrice isolated and unwilling to leave the Forbidden Library. Though she was instructed to wait for “That Person,” centuries of solitude caused her hope to fade. Encounters with those seeking only her knowledge worsened her loneliness, making her question her own existence. Her affection for Puck remained, but when she realized he had changed after meeting Emilia, her sense of isolation grew even stronger.

Upon meeting Subaru, Beatrice’s walls began to crack. Though she remained stubborn at first, she started opening up to others, participating in daily life at the Roswaal Manor and even showing concern for its residents. Through her bond with Subaru, she found the will to live again. When he refused to let her die alone, she chose him as her person and became his contracted spirit. Afterward, she grew far more cheerful and affectionate, proudly standing by Subaru’s side, showing warmth toward the Emilia Camp, and even teasing Otto like a sister would.

Beatrice is an artificial spirit currently contracted with Subaru, though she notes he is not a true spirit user. Due to her immense mana consumption, she once relied on draining mana from others within the Roswaal Mansion using the library as a medium. Now, her mana comes solely from Subaru, as she cannot draw from the atmosphere or restore it on her own. Through their contract, Beatrice can sense Subaru’s condition and location, and he can call her forth by focusing on their link. Despite these restrictions, she remains a powerful being with deep knowledge of magic, particularly Yin Magic, and has centuries of experience and wisdom.

A master of Yin Magic, Beatrice can perform teleportation, space manipulation, and powerful attacks such as Shamak and Minya. Her spells once allowed her to battle the Beast of the End and easily defeat assassins like Elsa Granhiert. However, after expending all her stored mana in the battle against the Great Rabbit, her abilities were weakened for a time. Even so, she remains capable of casting powerful barrier spells, gravity manipulation, healing, and curse removal. Having lived for over 400 years, Beatrice possesses vast magical knowledge taught by Echidna and stored within the now-lost Book of Wisdom, which once guided her before ceasing to show new content.

Beatrice is an artificial spirit created by the Witch of Greed, Echidna, over 400 years ago. Tasked with guarding Echidna’s mansion, the Palace of the Witch, she aided those who reached it alongside Puck. A few years after her creation, she and Puck helped Toska fend off the Silver Dragons led by Fargall. Later, she often accompanied Echidna to the Sanctuary, where she befriended Ryuzu Meyer. When the Warlock of Melancholy, Hector, attacked, Ryuzu sacrificed herself to complete the Barrier protecting the Sanctuary. Afterward, Echidna instructed Beatrice to link her library to Roswaal’s mansion using Door Crossing and wait for “That Person” who would one day free her.

For centuries, Beatrice remained in the Forbidden Library, meeting countless intruders who only sought her power or knowledge. Over time, her hope faded, and she began to believe “That Person” would never appear. Before Subaru’s arrival, Emilia and Puck moved into the mansion, though Beatrice soon noticed that Puck had changed, no longer the companion she once knew. Her long solitude finally ended when the strange boy Natsuki Subaru arrived, setting in motion the fateful meeting she had awaited for centuries.