It has been many years since Naota and Haruhara Haruko embarked on their adventure together. During this time, the conflict between the opposing forces of Medical Mechanica and Fraternity has escalated throughout the galaxy. Into this turmoil steps Hidomi, an ordinary teenage girl who doesn't expect much from life, until her school hires a new teacher named Haruko. When Medical Mechanica begins attacking her hometown, Hidomi discovers a special power within herself that only Haruko can help her unlock - a power that could save everyone. But why has Haruko returned to Earth? What became of the Rickenbacker 4001 she left behind with Naota? And where did the human-like android 'Canti' disappear to?