Rias is an easy-going devil who tends to be straightforward and bold in her behavior, including entering the boys' changing room without hesitation. Modesty and personal space are somewhat foreign concepts to her, and she has no issue with nudity (indeed being perplexed that people wants her to wear clothes at all). She always comes off as having a lewd streak, being extremely flirtatious and lustful with men she likes, and even says she feels ecstatic whenever she tastes/feels there bodies or saliva. She caresses, gropes, and simply cuddles with people she likes on a frequent basis, and can make out with people for hours when they are alone together with She finds draining men of semen immensely satisfying. She talks with people with hints of suggestive themes that always create misunderstandings, Despite this, she is careful not to let this get in the way of battle when fighting someone. Her playful and carefree nature shows even during fights, and she often teases her enemies and brags about her abilities. However, she is not too arrogant and often will take others advice. Rias is a beautiful young woman with a voluptuous body, white skin, blue eyes which she inherited from her father, Zeoticus, and a buxom figure. Her body measurements are B99-W58-H90cm. Her body weight is 128 lbs Her most distinctive feature is her long, beautiful crimson hair, which she also inherited from her father, that reaches down to her thighs with a single hair strand sticking out from the top. Her hair also has loose bangs covering her forehead and side bangs framing her face. Rias' height is 172 cm. Although Rias has worn various types of clothing throughout the series, her most commonly worn outfit is the Kuoh Academy girls' school uniform, which consists of a white long-sleeved, button-down shirt (short sleeves for spring/summer), with a black ribbon on her shirt collar worn under a black shoulder cape and a matching button-down corset, a magenta skirt with white accents, and brown dress shoes over white crew-length socks. Rias also tends to wear seductive lingerie and thongs, especially when she has a desire to sleep with someone she desires On some rare occasions, Rias wears glasses when she's deep in thought, as she feels they make her mind work better despite having perfect eyesight. As a Devil from the House of Gremory[2], 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 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

Rias loves participating in Rating Games, as she dreams of becoming the Rating Game champion by defeating the current Rating Game champion; Diehauser Belial, with the help of her peerage. While Rias is a powerful devil in her own right, being much stronger than average High-class Devils and according to Azazel, being able to become a Ultimate-class Devil just on the virtue on her talent alone, Rias suffers a bit of an inferiority complex when she compares herself to her fellow Rookies Four colleagues, as she feels inferior to Sona as a strategist and that she is far weaker in power than Sairaorg. However, according to Riser and Azazel, Rias has a talent for finding and recruiting talented individuals for her peerage, inspiring great loyalty. Rias is competitive and hates to lose, especially after losing her first Rating Game against Riser as she strives to always win, whether it is in sports or Rating Games. Due to being spoiled by her father Zeoticus and her brother Sirzechs.