For the observation and obliteration of this "fourth primogenitor", the government and Lion King decided to dispatch an attack mage referred as a "swords shaman". However, for some reason, the one chosen for the observation was an apprentice "swords shaman" girl, Himeragi Yukina.

Wielding the strongest anti-primogenitor spirit spear, Yukina arrived at Demon Sanctuary, "Itogami City". What was the true identity of the "fourth primogenitor", Akatsuki Kojou, she encountered over there!