I’m the Only Monster Tamer in the World and Was Mistaken for the Demon Lord

Sekai de Tadahitori no Mamono Tsukai: Tenshoku Shitara Maou ni Machigawaremashita

After a long journey, Noa finds the "Class Change Book." He's done to all to abandon his bothersome "Hero" role and gain a new class... "Monster Tamer."

(Source: MANGA UP!)