Sainoshi, a town surrounded by three mountains including Sainoyama. Izumi Shio's peaceful life is completely changed by her off-season transfer. The beautiful inhuman being who attacks her when she's lost in a mansion. The twin werewolves who save her life. Her brother's secret that comes to light. "Walpurgisnacht… It's a festival held on April 30 in Central and Northern Europe, to celebrate the boundary between spring and winter. People say it's the night when the boundary between the dead and the living is weakening. …yes, it's tonight." Walpurgis no Uta On the boundary between the worlds of the dead and the living, the girl finds a life-risking love.