One snowy day at her shrine, land god Nanami Momozono sees her familiar, the fox youkai Tomoe, collapse as dark marks spread across his body. After a long absence, Tomoe's former master, Lord Mikage, appears and places Tomoe into a magical pocket mirror to slow the progression of his affliction.
Mikage explains that long ago, before he and Tomoe met, the fox youkai was in love with a human woman. To live as a human with his beloved, Tomoe made a deal with a fallen god, but it only resulted in a curse that killed him. When Mikage discovered Tomoe, the god made the youkai forget his human love as a quick fix. However, something has recently revived the curse: Tomoe has fallen in love with his new human master, Nanami. With no way to stop the curse, Nanami decides to travel back in time to prevent Tomoe from ever being cursed, even if it means they might never meet. As she journeys hundreds of years into the past to save her precious familiar, Nanami discovers that her bond with Tomoe is far deeper than she ever realized.