He unlocks his hidden skills after training hard under four supreme masters.

[@BubbleCap7686]

The Ossan Newbie Adventurer, Trained to Death by the Most Powerful Party, Became Invincible

[@surmeet7805]

Anime name ???

[@androidboygaming9884]

Shinmai Ossan Boukensha, Saikyou Party ni Shinu hodo Kitaerarete Muteki ni Naru
Or
The Ossan Newbie Adventurer