Beatrice is the main antagonist and protagonist of the Umineko no Naku Koro ni series. She clashes with Battler Ushiromiya, trying to convince him that witches are real and that she used magic to execute a series of bizarre murders on the island of Rokkenjima. She has lived for over a thousand years. She has already strayed from the domain of humans, and it is said that as demons do, she appears when summoned by a human and lends him her power for a compensation of equivalent value. The things she likes are black tea and ice cream. The things she hates are boredom and people who deny her.
Beatrice appears as a Western-style woman with golden blonde hair and blue eyes. Beatrice has many different appearances in Umineko. Her witch form wears a bow adorned with a rose in her hair, a choker, and ballgown-like dress and wears the successor ring on her left middle finger. She is also sometimes seen holding a gold kiseru. Her human form wears a collared shirt with a cropped jacket and tie, a ruffled miniskirt, striped stockings, and boots and usually holds a cane with an eagle head as the handle. In End of the Golden Witch, she is seen as her witch form but with her hair down. In Dawn of the Golden Witch, her "chick" form is seen as her witch form, but her "elder sister" counterpart is seen as her human form but with her hair down.
As the Endless Witch, Beatrice has the ability to control life and death. She can repair damaged objects as well. Beatrice's remarkable ability is to take huge amounts of damage and survive, such as when she was impaled by several spears by Virgillia only to stand up and heal herself, though in the 4th game, she was "pierced" by Battler's blue truths and was "killed." Beatrice can summon several items such as the Stakes of Purgatory, which she mostly uses to carry out the murders in the island, the siesta sisters, Ronove, her butler, and goat attendants. Beatrice is also shown levitating in the air, teleporting, and turning into a swarm of golden butterflies. In the 4th game, she is shown burning Kinzo to death just by thinking about it. Beatrice is capable of summoning giants that would use shields of Hephaestus for protection. She also summoned "Shoulder Towers" which fired spears of light during her battle with Virgillia. In the meta-world, as well as the game board (Rokkenjima) she can use the red truth, blue truth and (most likely, being game master) golden truth. She is a witch in a beginner class, however she is said to be by Bernkastel such a powerful being that if she was fully aware of it no one would be a match to her, not Lambdadelta nither Bernkastel herself. Actually Beatrice might have unconsciously reached a level that surpasses that of witches and have become something even bigger. However Beatrice is known for her skillful use of Endless Magic to create any sort of illusion and her perfect mastery in creating and destroying the concept itself of eternity and infinity.
Beatrice is quite a controversial character. On the front Beatrice is a very cruel person, who loves to torture and kill people just for the sake of fun, a being so terrifying that even in the meta world she is feared from heavens to hell as one of the cruelest witches ever. She is at times very composed and majestic, and at other times very disgraceful and unsightful with a creepy laughter and a demonic smile. However, as the saga goes on more sides of her character are revealed. She proves to have a very joyful attitude and quite a childish side. She is infact described by her teacher as a naive child who loves to play with toys without the fear to break them and also with a power so big that she hardly realises she can handle. She shows this side primarly with Virgilia and Ronove which have a very parent-like attitude with her and less with Battler which she'd feel embarassed with to act so. Quite common is in fact to see her sobbing in Virgilia's chest when things don't go her way.
In the fourth game, Battler's blue truths "killed" her and she is unable to make anymore moves in the 5th game, which was replaced by Bernkastel and Lambdadelta. However, as Battler attempts to revive her, he loses to Erika Furudo's red truth and thus she died, fading into ashes, no longer waiting for him to solve the riddle she had laid out. When he tries to revive her for the second time in the 6th game as the new Game Master, his attempts are successful. However, the only thing that he revived was her body, and her soul/memories have been reset to "zero." Her personality is completely different than the former Beatrice. She speaks politely and refers to Battler as “Honorable Father”. This Beatrice wishes to help Battler with the game, so she goes onto the island and speaks to the portrait of her previous self. The Witch of Rokkenjima appears, and seems to be the same as the Beatrice that appeared in Turn of the Golden Witch, but with long hair; and she can only be seen by the new Beatrice. The revived Beatrice asks the Witch of Rokkenjima to teach her about the original Beatrice, and the latter complies. The Witch of Rokkenjima has no memories of the games spent in the meta-world, and only knows Battler Ushiromiya as a relative who had thrown away his last name for six years and returned. Later, it is revealed that the Witch of Rokkenjima can be affected by spider webs, while the new Beatrice cannot; and the latter can be affected by Natsuhi’s mirror, when the former cannot. Beatrice confesses several times in this arc that she loves Battler and was created for his sake. She also wants Battler to love her back. She even took the love trial given to her by Zepar and Furfur, where she decided to kill Natsuhi as the sacrifice for the first twilight. She was overwhelmed by Natsuhi's mirror but later Battler helped her. Near the end of Dawn of the Golden Witch, Beatrice attempts to solve the riddle to try to save Battler, who is at this point trapped. Once she does, Beatrice regains all of her memories. She immediately comes to rescue him from Erika, and challenges her to a duel where the loser gets shot. Beatrice wins, and she gets married to Battler (where her personality switches between the original Beatrice and the "zero" Beatrice), allowing him to remain as the Game Master. In the last few moments of the game, they both allow everyone on the island to obtain a happy ending. During Banquet of the Golden Witch, Rosa confesses she "killed" Beatrice about nineteen years ago. When Kinzo "trapped" her soul in a body, she lived in Kuwadorian, the hidden mansion. When Rosa got lost, she found the mansion and questioned why Beatrice lived there. In response, she reveals that "Kinzo told me there are wolves in the forest, so he put up the fence." After Rosa tells her there are no wolves, she takes her out of the "cage" Kinzo put her in.
They walk along a cliff (suggesting Beatrice escaping to the harbor, and getting off the island), but Beatrice stepped on weak ground, which collasped under her foot. Rosa notices her cry, and runs down to the bottom off the cliff's path, only to see Beatrice dead with her head possibly cracked open. Beatrice got out of that "cage"/body, and returned to the other witches, but lost her memory of that day. The events of Requiem of the Golden Witch suggest the Beatrice who died that day was likely Kinzo's daughter by Beatrice Castiglioni and the mother of Lion Ushiromiya.
- Beatrice's original name is uncertain, given Virgilia's former name was Beatrice as well and the name was passed down to Beatrice along with the title of Endless Witch. When Beatrice was young, Virgilia called her Princess, though it is unconfirmed if that was a title or a nickname. When Beatrice passes her name and titles to Eva-Beatrice, Battler continues to call to her as "Beato", the nickname that both he and Maria previously refered to her as, when she demands that he give her a new name.
- Beatrice's name is pronounced the Italian way, as "Be-a-tri-ce" (Be-a-to-ri-che [ベアトリーチェ] in Japanese phonetics) rather than the English way, as "Be-a-triss".
- Beatrice, out of eight characters, has had two Portraits of her featured in it.