After a young girl's mother dies she is moved from the city to the country where she accidentally meets a synthetic alien 'Figure' that takes the guise of a twin sister and begins attending school with her.

Tsubasa Shiina is a 10-year-old girl who recently moved to Hokkaido to live with her father. In school, she is very quiet and unsociable with her classmates. Then one night, she witnesses a UFO crash in the forest near her home. She rushes to the scene and finds the pilot, code named "D.D.", in a barely stable condition. Also in the scene is a Maguar, a hideous alien that hatched aboard D.D.'s ship. As the Maguar is close to taking Tsubasa's life, an alien life-form fuses with her body to form the Riberus battle armor Figure 17, which shortly destroys the alien threat. The life form takes the name Hikaru and turns into an identical twin of Tsubasa. As time passes, Tsubasa becomes more open to everyone around her, thanks to her new twin sister Hikaru. However, with Maguar eggs scattered all over Hokkaido, their ability to form Figure 17 is needed to eliminate all hatched Maguars until backup from D.D.'s home planet arrives on Earth.—ANN

Moving away from Tokyo and to a much less populated area, the young quiet girl Tsubasa must cope with making new friends. That's when an alien spaceship crash lands in her backyard. With aid from a living armour called a ribers, Tsubasa transforms into a bioandroid named Figure 17 and defeats the alien creature that caused the ship to crash here. The pilot, D.D. (as best as it can be pronounced by humans) thanks the girl and explains that several more of these creatures have escaped his transport ship and now reside across Japan. Upon separation from the ribers, Tsubasa stands face to face with a mirror image of herself, confusing both her and D.D. The ribers seems to have adopted her form instead of returning to its natural state. A very touching story unfurls from this chance meeting...—Anonymous