Moena Shinguji attends Bernard Academy in a dystopian future where humanity resides in floating cities above a polluted Earth. Orphaned young after her mother's death and father's disappearance, she was adopted by her aunt Kyoka, who operates a campus cafe. Beginning shy and reclusive, Moena gradually opens up through cafe work and friendship with classmate Hasumi, maintaining disinterest in romantic relationships.

Her life shifts when vivid dreams plague her, featuring an armored heroine battling mutants. Unaware of her link to these visions, Moena discovers a heart-shaped pendant that triggers her involuntary transformation into the powerful warrior Angel Blade. This armored identity possesses enhanced physical attributes and a revealing battle suit, wielding a signature sword generated from the pendant and summoning an "Angel Motor" vehicle. Initially, transformations suppress her consciousness during crises. After pendant damage in an early battle, Moena gains awareness while transformed, causing distress and embarrassment over the suit's exposure.

Psychic visions from the pendant reveal her parents created the "Angel System" enabling her transformation. Her mother explains Angel Blade's form is based on her own body, designed specifically to combat the Dark Mother organization. These revelations force Moena to reluctantly accept her protector role, struggling with the responsibility and the suit's nature. Her motivation surges when mutants kidnap her friend Seiryu Tenmyouin and later her aunt Kyoka, driving her to actively harness her powers for rescue.

Moena's abilities evolve through battles. Early encounters with mutants like Nailkaizer, Chloe, and Elaine demand rapid adaptation. Her Angel Blade form initially requires external intervention, such as maternal psychic protection manifesting as temporary energy wings and glowing eyes, to withstand powerful attacks. In later conflicts, particularly against the Widow, she unlocks gravity-manipulation powers vital for defeating enhanced foes. Yet, her effectiveness is sometimes compromised by emotional vulnerability during intimate contact, as when an influenced Seiryu incapacitates her through sexual stimulation.

Key relationships shape her journey. Moena admires Seiryu, deeply affected by his kidnapping and manipulation. She bonds with allies like police officer Ayame Fudo and fellow Angel-unit wielder Shaiya Hishizaki (Angel Ender). A pivotal development occurs with Elphie Elfman, a cowgirl who joins as Angel Beretta. After the Widow damages Moena's powers, Elphie helps reactivate them through intimate contact, triggering a vision of a winged woman hinting at deeper Angel System connections.

Central to her unresolved arc is the mystery of Dark Mother's leader, Phantom Lady. Evidence suggests Phantom Lady may be Moena's mother, Maina, under a "dark spell" her father referenced breaking. Kyoka recognizes Maina upon awakening in Dark Mother's castle. Phantom Lady's unexplained fixation on Moena and the Angel System further implies a familial link.