Maria is Rosa's daughter, and is the youngest of the cousins at nine years old. She has a habit of uttering 'uu-uu' at times, which frustrates Rosa greatly. Maria is also rather stubborn, and believes things easily, which isn't uncommon for someone her age. She has an interest in the occult, like her grandfather. She carries around a bag which is filled with occult items, such as a scorpion charm which wards off evil. She idolizes witches, and believes that they are there to bring people joy and happiness. In Maria's notebooks there are sketches of witches, and the witches are beautiful, fantastical creatures. It upsets Maria greatly when someone denies the existence of witches, especially Beatrice's existence. At certain times, Maria undergoes a personality change, and begins to laugh in an unnerving fashion. When she is in this mode, she acts rather condescendingly with regards to things about the occult, and will often call people like Battler 'stupid' for having little to no knowledge of such things.

She is the subject of bullying in her class, and the boys in her class often took her books and rubbed them off each other, saying that they got her 'germs'. However, Maria is content with being bullied. Maria came up with quite an imaginative story, where a horrid witch is terrorizing the school, causing students to get into accidents and the like. However, an angel offers one student as a sacrifice so that all the other students shall be safe. With that story, Maria doesn't mind being the subject of bullying, as she feels like everyone else can remain safe while she shoulders the burden.

Although she has no real friends, with Maria's vivid imagination, she breathes life into her stuffed animals. Namely, Sakutaro. Sakutaro was originally a stuffed lion cub, created by Rosa as a birthday present to give to Maria. Maria cherished it, and even though she was often alone, with Sakutaro she didn't feel as alone. However, Sakutaro met a tragic end when Rosa ripped him apart.

Maria is a rather innocent child, and fully believes that her mother needs to work such long hours and weekends. Rosa often forgets Maria's promises, but Maria says that her mother's work is more important. Rosa has told Maria never to call her work office unless it's an emergency. But, once when Maria called, the office told her that her mother wasn't at work. Even when Rosa takes impromptu holidays with her various boyfriends, Maria fully believes in her mother. Rosa often gives in to guilt, and ends up buying Maria presents, such as 'the rabbit band', or various Western sweets.

Maria as a witch
In the Umineko series it is heavily debated whether magic exists or not, but Maria has her own personal grimoire, in which she conjures up her own spells. Such as, 'have [x] for dinner', or 'make mama come home early'. One particular spell is for her mother's love, where all that is required is a simple 'uu-uu'. Maria came up with this spell after a rather touching day spent with Rosa on a picnic. Rosa taught Maria a song, and Rosa was so pleased that Maria knew the words. However, when Maria forgot the words, she started singing 'uu-uu' instead, but Rosa remained in her happy state. While Rosa thought that her saying 'uu-uu' was charming for a while, she eventually grew frustrated with it, and often resorted to hitting her. Whenever Rosa hits Maria, Maria says that she has been taken over by 'the black witch'.

Maria is a member of the Mariage Sorcière, an alliance of witches in which she and her idol, Beatrice, are exclusive members of. Despite having the same wand as Eva-Beatrice, she is not an Endless Witch successor. By succeeding to give a soul to Sakutaro, she is a potential Creator: a witch with an even higher rank than Bernkastel and Lambdadelta, who (when she will learn how to use her power) may be able to create even a galaxy from nothing. She is also the witch teacher of Ange, despite the fact that they did not see each other as she was banished from Mariage Sorcière.