Choukyoushi wa Mamono ni Kakomarete Ikiteikimasu. Yuusha Party ni Oiteikareta kedo, Densetsu no Mamono to Deai Saikyou ni Natteta

Ryu was left behind by his childhood friend's heroic party, who told him that they could not take a trainer with them. He runs a ranch in the village, but he spends his days feeling unworthy. One day, he saves a wolf from a trap in the forest...

The wolf he rescued was actually Fenrir, a legendary demon! The elder of the pack has lost his magical powers and has been looking for someone to help him. No ordinary trainer can heal him, but Ryu has magical powers that exceed even those of his childhood friend, the hero...?

After successfully saving the elder, Ryu learns how to handle the enormous amount of magical power that could destroy him. He is adored by Fenrir pack and becomes an extraordinary trainer!

(Source: Starts Shuppan, translated)