Rias Gremory is the main female protagonist of High School DxD. She is a Devil from the Gremory Clan - a family of pure-blooded Devils, and is known as the Crimson-Haired Ruin Princess. She is a third-year student at Kuoh Academy, the President of the Occult Research Club, and the school's number-one beauty as well as one of Kuoh Academy's Two Great Ladies.
Throughout the series, Rias is shown to be kind and soft to her servants. 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.She 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.She enjoys teasing Issei and Asia (from Volume 3 of the novels onward), but at the same time makes it clear (to Asia or any girl) that Issei is hers, and she does not want to share him (It is revealed in Volume 3 of the novels that the Gremory Family and their servants are beings with extraordinary affection among the Devils, so Rias is no exception). She has no problem with showing Issei her breasts or sleeping naked with him (which she always does according to her).
Rias is the daughter and second child of the Gremory Family. She became the heir after her brother, Sirzechs, became the Satan Lucifer, losing his right as heir to the house. After being announced as the heiress of the Gremory Clan, Rias was eventually placed into an engagement with Riser Phenex. Prior to the series, Rias has reincarnated Akeno Himejima, Yuuto Kiba, Koneko Toujou, and Gasper Vladi as members of her peerage. She entered Kuoh Academy two years before the series along with Akeno, Sona, and Tsubaki, reviving the abolished Occult Research Club which is used as a base for her servants and became its president.
From her mother, Rias has inherited the Bael Clan's Power of Destruction. This power allows her to release energies that can disintegrate matter, both living and inanimate, with relative ease. Opponents who wield sufficiently greater power, however, can shield themselves from this. In Volume 14, after her training with Akeno, it is revealed that Rias perfected a special one-hit kill move which is described as a compression of unimaginable amounts of demonic power. It has the appearance of an enormous sphere with a mixture of crimson and black aura radiating from inside of it. Rias claims that she created it by solely concentrating on destruction and strengthening it, after having experienced the constant assaults from the terrorists and the death of her beloved. The extent of its power is unknown but it is stated to be extremely dangerous, with its power surpassing the retiring system in the Rating Game.Rias has all the common skills and powers of a Devil. She is also shown to be at least somewhat proficient in the use of spells, such as the ritual to drain energy from Issei's left hand to let it appear human again, healing, teleportation by magic circle, and others. As a sister of Satan, the light novel hinted that her power is high compared to other Devils at her age. In Volume 1, she and Akeno are able to defeat three Fallen Angels with relative ease. In Volume 3, with a 8-time boost from Issei, she is able to force Kokabiel on the defensive. Although it is blocked, Kokabiel is not completely unharmed either. In Volume 6, Azazel shows a graph of abilities for the young Devils that is based on the four categories of Power, Technique, Support, and Wizard, along with an additional category, King. It is shown that Rias excels more in the Wizard and Power categories while averaging in both Technique and Support. Her quality as King is shown to be fairly high. Rias has gained the ability to project a red light from her breasts, which recharges Issei's energy. Each use of this power causes her breasts to temporarily shrink in size, which makes Issei cry even though it's sometimes necessary. Her breast size will restore itself after a few days of rest.
- Hero Wiki