As Queen Mashiro unveils her newly restored castle, the slave forces of the Schwarz descend upon Windbloom. It falls to Arika to defend the queen when all Otome are called to battle. Nagi steps forward to claim responsibility for the attack, while doing so he chooses his personal Otome. Presented with the cursed GEM, the Ultimate Black Diamond, Nina must make a fateful decision between friendship, loyalty and love. What fallout will her choice hold for those that are dear to her?