Sono Yo no Dokoka, Souten no Yurikago

Shin, the third-born prince of the great kingdom of Garche, has lived with his servant Liandros since he was born... and now, Liandros has disappeared. Lia remained loyal despite Shin's "adventures" around the world and all the trouble he'd gotten them in. Unexpectedly shaken by this turn of events, Shin tracks Lia down to the small village of Barako on the fringes of Garche, where ancient religious structures still stand. There, he finds that Lia is receiving some sort of treatment from a suspicious so-called "shaman," and refuses to come home. That's when Shin starts to come down with a mysterious disease specific to the region... (Source: Renta!)