Brook

Eris Boreas Greyrat

エリス・ボレアス・グレイラット
She is Rudeus' older cousin and also his student. When Rudeus was around seven years old, he taught her magic along with math and reading. She is a violent, strong and proud girl and merciless towards anyone who holds negative emotions and intentions against Rudeus. (Source: Mushoku Tensei Wiki)