Regarding her rosy lips and noble eyes colored purple, the Princess Knightess of the Kingdom Rastalia gains popularity among her people. She has proficient art of sword combat, often involved in fighting against invading military forces. One day, she is informed that one of her retainers is summoning monstrous creatures in a castle which is located far away from the towns. Given the townspeople are threatened by the creatures from the castle, the King orders Aries and her soldiers to investigate the castle but... She falls in a deep pitfall, that isolates her from the other soldiers. Beating confronting creatures down, Aries heads for the Phantom Castle.