Saiyuuki

Genjo is a Buddhist priest in the city of Shangri-La, which is being ravaged by yokai spirits that have fallen out of balance with the natural order. His superiors send him on a journey far to the west to discover why this is happening and how to stop it. His companions are three yokai with human souls. But this is no day trip—the four will encounter many discoveries and horrors on the way, and on the road, Genjo will wonder … can he really trust his supernatural companions?

(Source: Kodansha USA)