Due to an inexplicable incident, Toono-kun's life has spiraled out of control. While his younger sister Yayoi was participating in a track and field event in the schoolyard, a sudden flash caused multiple injuries, including Yayoi's. Fortunately, Yayoi was discharged from the hospital the following day, but she behaves in an unusual manner. Toono has come to realize that his sister isn't herself but instead is a soldier named Luca from 31 years ahead in time. Remarkably, Toono is the only one aware of this bizarre occurrence.
