Tsubasa is a shy elementary schoolgirl with very few friends she has just moved to Hokkaido from Tokyo with her father, leaving her friends behind. One night, she sees a shooting star and follows it to witness an alien space ship crash. Unfortunately this ship was carrying a dangerous cargo, which has escaped. The resulting encounter introduces her to DD, the alien pilot, and the Riverus - an intelligent, sentient alien armour - which merges with her and creates a clone named Hikaru. Hikaru is as outgoing as Tsubasa is quiet. As Tsubasa teaches her new companion about the world, she rediscovers it herself. When unfriendly aliens begin to appear, Tsubasa and Hikaru unite to form the Figure 17, a bio-humanoid combat system.