*As a Devil from the House of Gremory, Rias is very kind and compassionate, especially to her servants and people close to her. She gets angry and violent whenever people insult her or her peerage, showing a fiery side to her. This also plays into the fact that she dislikes cruelty towards people, as shown with her disgust over Marius Tepes, who abused his own sister for his own benefit, and how she killed the Fallen Angels, such as Mittelt, Dohnaseek, Kalawarna, and Raynare for their cruel treatment of Issei. Rias also holds great sympathy towards Sairaorg and his mother Misla Bael for how badly they were treated by the Bael clan.

Rias is proud of her family's name, but she does not like being seen as Rias of the Gremory Family. The reason for her living in the human world (as revealed in Volume 2 of the novels) is because there, everyone sees her as Rias, not as a Devil or as the Crimson-Haired Ruin Princess. Due to this and the fact that the only men who showed interest in her were interested in her due to being the Heiress of the House of Gremory, Rias soured on the idea of finding a lover, until meeting and falling in love with Issei.

She thinks of Issei as a special person and always gets jealous when girls are around him, becoming a totally different person when she sees him and other girls together, or when it comes to training. Despite her mature stature like a woman, Rias tends to act her true age and becomes frustrated whenever girls flirt with Issei. While Rias is usually calm and mature in most situations, she loses her mature aura and presence when she sees any girl (especially Akeno) flirting with or seducing Issei.*