It's the Heian era, a time of peace, of Japanese cultural aristocracy, national identity, and pursuit of beauty through art and poetry. A long-forgotten race, the Hotaru-Raiko, as they have come to be known, part human and part firefly, dwells secretly alongside man. This noble clan once lived near the tree of life. Now they make their home in a thicket near the Fukui Castle moat in the Echizen Province, just north of the capital in Kyoto, Japan. Often mirroring man's culture, they are particularly fascinated by the budding "way of the warrior" philosophy. However, in this time of peace, a foul creature escapes the bottomless pit, and a traitor emerges among the clan. Seduced by a spider yokai seeking to release an army from the abyss, the traitor helps form the treacherous Tsuchigumo clan. With their help, the temptress is able to assassinate the Hotaru-Raiko lord and his faithful samurai. In the wake of this devastation, the daimyo's eighteen-year-old daughter is tasked by an angel to defeat the spider yokai, destroy her traitorous clan, and raze the Abaddon gate to the ground. Can she rise through the grief to lead the remnants of her father's army as onna-musha? Who will stand by her side? What gift does the angel bring her? Will the Hotaru-Raiko find the gate to the abyss and complete their quest in time?