One day, Mio (Yume Nikaido) learns that her older sister, Tetsuko (Moe Tenshi), has been using the "Hadaka-ken" technique to protect the family home all by herself. After witnessing Tetsuko's failure to use the "Hadaka-ken" against a powerful opponent, Mio decides to learn the "Hadaka-ken" herself and fight. Will Mio be able to avenge Tetsuko's death?