Tsubasa Shiina is a shy 10-year-old who has recently moved to Hokkaido to be with her father. Due to her introverted personality, she rarely interacts with other kids. However, her life takes a sudden turn when she witnesses a UFO crash landing near her home in the forest. Upon investigation, she stumbles upon the injured pilot, known as "D.D.", and a fearsome alien creature named a Maguar that was on board the ship. When the Maguar approaches Tsubasa, she is in peril, but an alien entity merges with her to create the formidable Riberus battle armor Figure 17, defeating the alien threat. The alien entity, resembling Tsubasa, is named Hikaru. Eventually, Tsubasa begins to open up and connect with others due to her newfound counterpart. However, with Maguar eggs scattered throughout Hokkaido, Tsubasa and Hikaru must create Figure 17 to destroy all hatched Maguars until D.D.'s planet intervenes.