Figure 17: Tsubasa & Hikaru

Tsubasa Shiina, a reserved 10-year-old girl, has just relocated to Hokkaido to stay with her father. Struggling to connect with her classmates, she often keeps to herself. One fateful night, however, her life takes a drastic turn when she witnesses a UFO crash in the nearby woods. Curiosity leads her to the crash site, where she discovers a wounded pilot known as "D.D." and a terrifying alien creature called a Maguar. Just as the Maguar threatens Tsubasa's life, an alien entity merges with her, granting her the powerful Riberus battle armor, Figure 17, which she uses to defeat the alien menace.

As Tsubasa navigates her new life, the alien life form, now taking the form of her identical twin sister, Hikaru, helps her grow and open up to those around her. Together, they face the challenge of eliminating the scattered Maguar eggs throughout Hokkaido while waiting for assistance from D.D.'s home planet. Their bond deepens as they work together, blending the extraordinary with the everyday in a tale that balances action and the nuances of friendship.