As Yuna and Polylina sing on stage, their performance is interrupted by a young girl named Ayako who is the youngest of the 3 Dark Sisters which are set on eliminating Yuna and her friends. Meanwhile her friends are battling the other 2 sisters and she visits them in the hospital after many were defeated. The next day as Yuna leaves for school, she notices the building was demolished and the nearby hospital is being attacked. Ayako is once again causing destruction and as Yuna's friends try to control the situation, Yuna takes matters into her own hands.

After calming Ayako down and even befriending her, Yuna shows her what it's like to be a normal girl. Ayako begins to trust Yuna and has even offers to help in the mission to destroy her sisters, Genmu and Kyoka. As Yuna and her friends head into space to invade the sisters' ship, they learn of their plan to not only eliminate Yuna but to eliminate the Earth as well. The battle begins and Yuna and her friend must defeat the android sisters before their planet is annihilated.

After defeating Kyoka (the middle sister) and returning home, the surrounding city is attacked by the eldest and most powerful sister, Genmu. Ayako pleads with her sister to cease destruction on Yuna and the earth but her request is ignored as Genmu rips the life force out of her causing her to fade away. Yuna has become emotionally upset by the loss of her newest friend and with a new burst of energy, she fights Genmu as the battle comes to a close.