Character Name: EVA-Beatrice.
Character Series: Umineko no Naku Koro ni.
Character Age: Not stated specifically in canon other than that her looks are about Japanese middle school age, so let's say about 14.
Background: Ushiromiya Eva had a dream. A dream of stealing away the headship of the Ushiromiya family from her older arrogant brother Krauss. But no matter how hard she worked to show that she was capable of succeeding Kinzo as the head, she still wasn't Kinzo's firstborn, not to mention a woman. There was no way that Kinzo would ever let her succeed him. And so Eva developed another 'her' inside herself, another her that always convinced her to keep working and never give up so that their dream would be realised. She told Eva that she would help her with her 'magic' that turned anger into power, power that would help Eva succeed.
But as time moved on and Eva grew older, the other her inside her never grew. She remained the middle school girl that Eva had been when the other her had appeared to her. And even as Eva grew on to new dreams, a dream of happily living with her family and having her son George succeed Kinzo as the head, the younger Eva held on to the dream they had shared of Eva becoming the family head.
So when Eva arrived at Rokkenjima, an isolated island, for the annual family conference and an opportunity appeared to become the head, both of them immediately jumped on it. A letter appeared which stated that anyone who would be able to solve the witch' epitaph displayed under a portrait and find the gold it pointed to would become the head of the Ushiromiya family. Eva was able to solve it with the help of the other her inside her and found the gold. But what she didn't know was that along with the title of family head, another title was given away - that of the golden witch, Beatrice. Eva's younger self got a life of her own without Eva even noticing at first, being able to freely move without Eva. She inherited the title of the witch Beatrice from the old Beatrice, along with the Endless Magic, magic that allows one to kill and revive anything over and over. (Even though she inherited the title of 'Beatrice', she's usually called EVA-Beatrice to differentiate her from the original Beatrice.)
There was only one problem left, the new witch had to carry out the resurrection ceremony for the witch Beatrice that the previous Beatrice had started. Seven people still had to be sacrificed. But the new witch quickly discovered how much fun it was to kill people in the most absurd ways (drowning them in a sea of jelly, squishing them between layers of a giant cake, turning them into a butterfly and watching them get eaten by a spider) and reviving them over and over that it went out of control until the previous Beatrice stopped her, telling she had to carry out the murders with dignity according to the ceremony.
But there already was no saving it anymore. EVA-Beatrice figured that as long as she would make the last death be in accordance with the ceremony's rules, she could play with the sacrifices as much as she wanted before that. She quickly lost her respect for the old Beatrice and started ignoring her advice until she even attempted to kill Beatrice a few times. She also started killing more and more people, even more than the ceremony required because it was just too much fun to her. At the ninth twilight, the Witch shall be revived and none shall be left alive.
Finally Battler (who had been having a logic battle with Beatrice about the murders) was tired of it all and started a logic battle with EVA-Beatrice instead, claiming that she wasn't a witch but instead Eva herself killing everyone. But the new witch used the red truth (red text that only tells the 'truth', even though it could just be wordplay) to corner him so thoroughly that there nearly wasn't a possibility for a human culprit anymore. Battler was only saved from a huge loss by Beatrice who used the red truth to deny witches instead, denying EVA-Beatrice as well.
Personality: The more detailed here, the better. This lets us get a good feel for the character. Please try to back up your details with canon examples when you're getting past their basic character and more in-depth. Generally, we want to see at least four good-sized paragraphs.
There are quite a few sides to her.
Firstly it should be said that since she was first created by Eva as a sort of another her to talk to, she is a lot like Eva. She has the same determination to become head, perhaps even more than Eva does. Becoming the head is the dream she shares with Eva and she won't stop for anything to get it to come true. When Eva displays the slightest hesitation at whether they'll succeed or not she immediately gets angry at her for betraying her dream and the same thing counts for when Eva shows signs of wanting to exchange her dream of becoming head for the dream of letting her son George become the next head instead. Even though Eva changes her mind, EVA-Beatrice won't stray an inch from the goal of becoming head. She's also shown to be pretty smart, even though she looks like a middle schooler. It was only due to her help that Eva was able to solve the epitaph that nobody was able to solve before, not even the people who are shown as generally smart from the family. She's eager to learn things (especially about her witch powers) and seems to want to tackle problems on her own head-on. Somewhere during Episode 3 she tells the old Beatrice, "My motto is to study things myself before asking other people." The only person she relies on is herself.
But just like Eva (and about everyone else in the Ushiromiya family, honestly) she isn't an exactly nice person. She literally wouldn't stop at anything to reach her goals, no matter who she has to walk over in the progress. Another quality she got from Eva was Eva's sharp tongue, EVA-Beatrice is quickly to critisize things and especially people. She doesn't speak good of people easily but seems to think lowly about nearly everyone instead. At one point she tells Eva that "men are always children", calls the riddle nobody else could solve infantile and is calling people idiots and all sorts of other things left and right. Usually she's thinking lowly of people because she believes they're all just slacking around, because in her eyes nobody is putting as much effort in reaching their goals as she does. Her catch phrase already says enough about her, she's constantly saying 'why don't you shut up and die?'. If people don't put in enough effort they might as well shut up and die or cry themselves to sleep and die in her eyes.
She is, however, able to care about people but the only person she ever cared for in her canon is Eva. And that was most likely just because they were the same person. At first she's not just becoming head for her own sake but mostly for Eva's, even as they grow apart in age and thoughts she still helps Eva realise her goal using her 'magic'. Even when they are seperated she still offers to let Hideyoshi and George (Eva's family) alive while killing everyone else. It isn't until Eva starts protesting against her actions that she decides that they have nothing to do with each other and she kills those two nonetheless. But she wasn't super nice in her way of supporting Eva from the very start: she was telling Eva to shut up and die if she stops trying just like she does with everyone.
But the biggest and most noticable distinction between her and Eva is the fact that she's still a child. EVA-Beatrice never quite grew up from being a middle schooler and is still very childish. She throws tantrums that are very reminiscent of little children when she doesn't get what she wants. Most of the time this happens because she's very greedy. When she and Eva discover the gold she isn't planning on letting anyone else get even a slight portion of it, even when Eva herself is willing to share it with the other siblings. When Eva proposes a plan to cheat Krauss out of money by blackmailing him about the embezzlement EVA-Beatrice calls it 'boring'. She longs for entertainment and exciting things like most kids.
In fact, her own dream (that isn't Eva's dream anymore since she grew up) has been to become a witch all along. At first she's so surprised and intimidated by her promotion for witch that she's uncharacteristically humble and quiet when it happens. It's noted that she even has an 'embarassed smile' on her face as other witches and furniture congratulate her with her new status of witch. That quickly turns to what Battler in his narration calls 'an innocence which reflected upon her own joy'. She truly is like a little kid that just got her dream granted, she's honestly happy her new status and magic. The problem lies in giving power to young people; they're usually not able to handle it. It doesn't take long for EVA-Beatrice to get obsessed by her new powers and she starts abusing them horribly, killing people in the most gruesome ways just for fun. She even remarks when someone calls her out on it that "it's like playtime that never ends!", showing that through all of it she is still like a child. When you break a toy, you might not be able to repair it to its original state, but with the Endless Magic she can break and repair toys over and over again all she wants. The taste of that taboo drives her mad, even to complete temporary bouts of insanity. It's mostly a clear example of how power corrupts.
It should be noted that at first EVA-Beatrice did have great respect for the previous Beatrice, she even kneels for her the first time they meet. She did look up to the witch since she had heard about her power and cruelty and wanted to become just like her, but the more Beatrice starts complaining about her behaviour the more EVA-Beatrice starts to dislike her up to a point where she tries to kill Beatrice. It's reflected in her way of addressing her, at first she still calls Beatrice 'precedessor-sama', but later on it turns into 'granny'. It's partly her childish side throwing another tantrum at stupid older people denying her her fun.
Abilities: EVA-Beatrice is a witch and is therefore able to use a whole slew of magic. Like all witches in the world of Umineko no Naku Koro ni she's shown as being capable of teleporting. Other powers she has shown are flying, levitating others, making things appear out of nowhere (giant cakes, seas of jelly), transforming others (turning Rosa into a butterfly) and transforming herself (in Episode 4 she transforms into Eva). She interherited the Endless Magic from Beatrice, which allows her to kill and revive people over and over again as she pleases. She is able to summon the Seven Stakes of Purgatory, seven magical girls that can turn into stakes to kill people. Her own preferred servants ('furniture') however are the Siestas, bunny-girls that shoot off an infinitely long golden 'arrow' (string) that can pierce people and kill them. EVA-Beatrice is also shown as being able to use the red truth, which is practically just red text that is used to state the truth (although worldplay can be used in it) in Umineko's logic battles.