Haruka Minazuki and Aoi Kannazuki are best friends and students at St. Cherine Academy. By day they lead ordinary school lives, but when danger arises they transform into the magical guardians known as the Twin Angels: Haruka becomes the energetic Red Angel and Aoi the composed Blue Angel. Their primary mission is to recover the fragments of the Holy Grail, a set of seven magical amulets that have been stolen by the villainous organization led by a man called Black Trader. The amulets, when assembled, possess immense power, and Black Trader and his subordinates, including the twin assassins Tesla and Nine Violet, will stop at nothing to claim them.

The manga follows Haruka and Aoi as they balance school and secret heroics, facing a series of enemies sent by Black Trader. Early in the story, they are joined by Kurumi Hazuki, Aoi's energetic cousin, who becomes the White Angel. Together, the three Twin Angels track down the amulets while also confronting personal doubts and deepening their bonds. The narrative later expands to include a new threat: the Black Fund, an evil organization that steals a powerful artifact called the Tears of an Angel. The Twin Angels, now including former enemies Tesla and Nine who have switched sides, must launch a final battle to reclaim the artifact and bring peace. The manga concludes with the Twin Angels successfully defeating the Black Fund, though not without sacrifices, and returning to their everyday lives, their powers and friendships tested but stronger.