Ore no Zense no Chishiki de Teihenshoku Tamer ga Joukyuushoku ni Natte Shimaisou na Ken

Tamer. This fantasy profession cultivates relationships with almighty monsters, boasting abilities to make even the greatest hero weep in wonder. One such tamer, famed for the power of his companion beasts, gets caught up in an incident involving storage magic and is reborn into a totally different world as a youth named Varius.
Here, he's faced with a terrible change to the status quo: tamers are seen as nothing but the lowest of the low. "I'll never let you insult tamers again!" Varius sets out to prove that the tamer really is the ultimate profession. Thus begins the story of the overpowered tamer who seeks to overturn the very foundations of his world!
(Source: One Peace Books)