Nicknamed as Tomboy Princess, Princess Rubiria is the daughter of the First Queen of Sternbild Kingdom.
She was first introduced when she was kidnapped by "thugs" in Trient and rescued by McCool Say with the help of Rou. She then employs Rou to escort her back to the Royal Capital. She later employs Rou to train the palace guards as well as help her stop a coup d'etat.
Because of her unusual prowess at mind reading, Rubiria was confined inside of her Amber Palace until she turned 12. This has caused her to discern the dark sides of humans and only trust a few. This along with a spoiled upbringing has caused her to become arrogant in not only herself but her ability despite the fact that she still remains quite naive due to her limited experience in the world (as noted by Rou). Upon meeting Rou, she becomes shocked that he does not treat her as a princess but rather as her superior. When she realizes his abilities are vastly greater than any in her Kingdom and that she cannot read his mind, she becomes strongly attached to him. In order to gain his favor, she becomes less arrogant and begins to stop talking down to others. She has developed a habit of repeatedly riding on his shoulder whenever they meet. Even when they're separated, Rubiria is constantly contacting Rou and coming up with cunning ways for them to spend time together, going so far as to hire him to train her palace guards.
Rubiria has the typical appearance of a twelve year old girl. She has a thin, fragile-looking constitution to the point Rou believed she might break if he touched her. Her hair is platinum, and is considered by Rou to be quite beautiful.
- Mind Reading - It was revealed on Day 170 that Rubiria has the unique ability to read people's minds. This ability was inherited from her royal bloodline. Despite the fact that this ability has diminished in the royal family, the power is especially strong in not only herself but her mother (Albeit, her mother can only read minds when she has eye contact with others). However, she is unable to read Rou's mind and can only discern the intentions of the members of Parabellum.
- 【God of Judgement's Divine Protection]