Scarlet Soul. Volume 3
Two sisters, Lys and Rin Shirano, watch over the Hundred Altar Gate that maintains balance between the worlds with the help of the Sword of a Hundred Souls. But one day, Lys disappears suddenly, and the sacred sword she left behind reacts oddly to a mysterious phenomenon. Accompanied by the demon Aghyr, young Rin sets out on a quest to find her sister through a kingdom that's once more under threat. This is volume 3 of the series.