"Is that note of light or of darkness?"

GARO Side Story: The Tougen Flute (2013)

Long ago, a fallen Makai Priestess named Higari became too powerful and after tampering with powers no one should wield, she had to be stopped and was eventually sealed away by another Makai Priest named Sougen. Using his body and his own life, he created the Tougen Flute and sealed Higari shortly after his death. However, through a special ritual, those who seek Higari's power can resurrect her by replaying eight notes on the Tougen Flute to undo Sougen's seal. In the present, while Kouga Saezima has travelled to the promised land (Garo: Soukoku no Maryu), two fallen priests,Jabi and Rekka, will attempt to return Higari.

TFC · Omnibus Japan