During a morning of bliss, Kū in the midst of a quest to understand the depths of Setsuna's emotions. Battle preparations are drawn up in anticipation of the threat of Batraz and Kyoshiro decides to bring Kū to his old academy.

After Kyoshiro was injured in a fall from a cliff, Kū tends to his wounds for the time being despite there's nothing much she can do. Once Kyoshiro wakes up, he tells Kū about the brother he idolizes and the sacrifice he made ten years ago.

Kū and Kyoshiro head to the market for some pleasant shopping, and afterwards a transformed Kaon is sent to kidnap the unsuspecting girl, and new startling revelations lay out Kū's destiny.

Once discovering that she is the fifth Absolute Angel, Kū is all but ready to combine with Kaon which would in effect make Kū disappear. Before this can be accomplished, however, Setsuna and Tarlotte show up and battle with Kaon.

After Kū is rescued, she starts to wonder what to do now that she knows she's an Absolute Angel. She eventually tries to activate her powers, but is unsuccessful at doing so. Meanwhile, Kyoshiro is battling latent feelings for Kū despite having the desire to destroy all Absolute Angels.

Kyoshiro prevents Kū from falling to her death off a tower. He then confesses his love for her and promises to be with her after he takes care of Setsuna's feelings. However, Setsuna witnesses the events and breaks down emotionally. Valteishia suddenly appears with Kazuya and interrupts the standoff.

Upon reentering the world, Kazuya carries out his agenda against his own kin and proceeds to claim the Absolute Angels for himself.

Kazuya captures Tarlotte and proceeds to reunite all five Absolute Angels in a mock wedding ceremony to create the Bastille. Kyoshiro, Sōjirō, Himiko, and Jin's squad fight their way toward the Bastille to rescue the Absolute Angels.

Kazuya commences the rebirth of his lovely Cielo. Sōjirō, Jin, and Himiko fight off the soulless Steel Angels while Kyoshiro races toward Kū. Within the Angel Gallery, Valteishia confronts each of the Absolute Angels about her deepest wish. The vessel for Cielo, Bastille, is reborn but rebels against Kazuya as the Absolute Angels regain their own wills. Kū is reunited with Kyoshiro and regains her memories of him.

The Bastille releases the Absolute Angels, who are reunited with their respective partners. Kazuya's ambitions for Cielo are crushed. The destruction of the Bastille, however, costs Kū her life. Kyoshiro promises her many things to do 'the next time around' before all of her mana is drained away. The world returns to peace and Kyoshiro and Setsuna embark on a journey to find Kū's reincarnation, which they do succeed in years later —— This is shown after the credits when Kyoshiro and Setsuna find Kū.