One day, the peaceful life of mankind came to an end because of the invasion of a creature called "beast". When the last human, William (voiced by Ryohei Arai), woke up from his deep sleep, he found that 500 years had passed, and William carried the last hope of human continuation. The only fairies in this world who can compete with beasts are those who know how to use holy swords. However, these fairies turn themselves into swords, and once their energy is exhausted, they will face the tragic end of death. Under the operation of the gears of fate, William met the fairies. With the help of the gentle and considerate Chtholly (voiced by Azusa Tadokoro), the taciturn and self-willed Nephrine (voiced by Akari Uehara), the seemingly ignorant but actually unfathomable Essia (voiced by Machico), and the straightforward and straightforward La Entoluco (voiced by Kazusa Arami), can William take back the territory that belongs to humans?