Modern society is in state of peace and prosperity thanks to advancements in civilization and science. Sumiki Sumi, a female student attending the Goeiji Academy, lives alone in the school's dormitory after losing her parents at a young age. One day, she encounters monstrous beings attacking humans. Despite her fear, Sumi decides to save people from those hideous things. In this time of crisis, a plush-like creature named Kuunerii appears before her and gives her an item called a Light Gear. Sumi is chosen by the Light Gear called Alexandros, and transforms into the hero of light, Arch Brave. She decides to confront the invading demons known as the Arch Erimos with her newfound powers. Meanwhile, Ladiesthor is leading the demons' army and decides to obtain the newly transformed Arch Brave.