The series melds together several elements both familiar and new. The majority of the main characters appear to be involved in romantic relationships. KÅ« is often struggling to make sense of who is truly in love with whom. A large amount of kissing is witnessed very early in the series. The Absolute Angels are superhuman in nature and to remain so they must draw energy from a human being through the lips, a theme borrowed from Steel Angel Kurumi.

The series breaks from the regular battle etiquette in which the pilot of a mecha climbs into the cockpit. Rather, the Angels materialize and control their mecha from without or manifest specific parts of their bodies into large mechanized limbs. Throughout a battle, an Angel phases in and out of their angelic forms voluntarily and involuntarily. As in Kannazuki no Miko, the names of the mecha are taken from artifacts and iconic figures of Japanese and European mythology..''

Kū is quite the normal high school girl who feels as if she is drifting through her existence and she always describes herself as being "empty". She never misses a chance to give letters to the mysterious prince in her dreams and frequently talks to him in her thoughts. In reality she is an introverted girl, believing that she lacks good qualities. She appears to be easily overwhelmed by situations that deviate from her previous experiences and expectations. Her original name is Cielo (チェーロ, Chēro?), meaning sky, who is the original Absolute Angel researched by Kazuya and his grandfather. During the incident ten years prior to the main story, Cielo is split into four pieces, Murakumo, Batraz, Claíomh Solais and Megingjord. In addition, Megingjord is separated into two pieces. Kū is the original body, while Valteishia is the soul; this explains Kū's initial feelings that she is lacking something inside. In the end of the series, her body crumbles and she reincarnates as a smaller version of herself. After the credits of the last episode, Kyoshiro and Setsuna find her near the European Alps, and when she sets her eyes on Kyoshiro she instantly remembers her past life's memories. Her personality and characteristics are drawn heavily from Himeko Kurusugawa from Kannazuki no Miko, meaning that two distinct characters are inspired by her.

Kyoshiro is instantly likened by Kū to the prince in her dreams when he transfers to Kū's school from the legendary Jōtō Academy. He is a refined gentleman, adept in horseback riding, and has a tendency to play the violin while deep in thought. Kyoshiro is the youngest of the four children in his family. He supports the Central Student Government and has also stated his intention to recover and destroy all of the Absolute Angels, following what he believes to be the wishes of his deceased brother, Kazuya. He eventually falls in love with Kū, which forces him to re-evaluate his belief about Absolute Angels and the way he has been treating Setsuna. He later admits to Setsuna that he loves Kū and, albeit after some time, Setsuna understands and only agrees to Kyoshiro's plans after she accompanies him to find Ku and says her farewells.

Setsuna, also known as "Setsuna of the Moment of Dreams," is the Absolute Angel Claíomh Solais (Kurau Sorasu). She fights alongside Kyoshiro as his partner. Setsuna treasures a ribbon bow with bells, which is given to her by Kyoshiro and tied to the right side of her headdress. Rarely expressing any emotion, she is physically beautiful and can carry out every household chore flawlessly, leading Kū to call her a "princess". Setsuna acts solely based on Kyoshiro's orders and wishes, not her own will, and has a habit of saying, "Would you prefer that, Kyoshiro?" She begins to grow jealous of Kyoshiro and Kū's closeness, but she holds back her feelings so as to not trouble Kyoshiro. When Kyoshiro confesses his love for Kū, however, Setsuna fails to restrain her emotions for the first time. In special three of the anime, Setsuna started to copy Kū's actions so she gets Kyoshiro's love and kindness. She later understands Ku's feeling and lets Kyoshiro love Kū. She later accompanies Kyoshiro, after cutting her hair, to find Kū and say her final farewells. She most closely resembles Otowa from Kannazuki no Miko. Setsuna's Absolute Angel symbol is located on her right arm, which is the dominant hand in Claíomh Solais.

Voiced by: Atsuko Tanaka (Japanese), Kaytha Coker (English) Mika is the ruler of the Higashigetsu Fūma Witch Academy, who is setting forth the domination of all the female students through her right hand, Kaon. She displays signs of jealousy fueled by possessiveness when observing Himiko providing Kaon with energy, and apparently has a vindictive streak, as she punishes those of her subordinates who fail her. Furthermore, she displays signs of megalomania and extreme egomania[citation needed]. Mika is the third eldest child of the Ayanokōji family. She seems to have heterochromia, with her right iris being purple and the other orange; it is later implied that the orange eye may in fact be an implant. Mika suffered injuries during the 'Days of Hot Snow' which obliged her to have hospital stay and she is shown with a bandage covering her left eye. Years later, she seems to be suffering from a potentially debilitating medical condition, despite her usual poise and her much-lauded graces, which is possibly exacerbated by her tendency to provide Kaon with too much of her own Mana.

Mika's own words betray that she desires Murakamo to love no one but herself and she expresses a malicious jealousy and contempt of Himiko, who is much deeper in Kaon's affections than she can apparently hope to be. Mika's flashbacks to her time in the hospital imply that she has fixated on Kaon because Kaon reminds Mika of a similar-looking nurse, who had cared for Mika while she was injured. Other people who bear the brunt of her bile are her elder brother Kazuya, whom she hates absolutely for everything he ever did, including the events surrounding his supposed death, and her younger brother Kyoshiro, who she considers to be 'the demon's tail', with Kazuya being 'the demon'. Mika's intense hatred for Kazuya seems to have originated during her early teens, when he stole away a girl she was developing an affection for, apparently with the explicit intention of hurting his sister's feelings.

Before her death, she entrusted Himiko to rescue Kaon from Kazuya, despite the fact that she hated Himiko because of her closeness to Kaon, and to that end gave her the key to a device she created based on plans drawn up by her grandfather Reitarō. This device is a cello capable of creating a harmony to suppress Mana, thus causing pain to an Absolute Angel—or Kazuya.