Beatrix is the youngest of the 'Sibyl Sisters' who all have a deep connection to The Unda. She runs her own mod shop, “Beat Frequency”, which supplies Muses with their weapons. Since Cyrus can vibe with any mod, he can use any weapon Beatrix has available. The most basic version of each weapon type is available at the beginning of the game, but new, stronger models can be purchased or upgraded as the game progresses.

For clarity, the weapons on display in her shop are all props, since her mods only manifest real weapons in The Unda.

Having been around Muses for so long, she's developed a deep fascination with The Unda and is always eager to learn more about it. However, after losing both of her parents and nearly losing her oldest sister, she's also deeply terrified of it. She's in deep denial about this fear and has never truly come to terms with her parents' deaths, so she uses her enthusiasm as a way to cope and cover her true feelings. Once Cyrus is able to help her work through her trauma, her moods become less extreme (although she never loses her enthusiasm), and Cyrus is able to recruit her as a party member.

In combat, Beatrix uses a scythe and can learn a number of Frenzy attacks (such as Frenzied Slash and Frenzied Whirlwind) that make her considerably useful for crowd control.