Is it the one where MC is a mage, and the Hero mistreated him like most tsunderes do so he left. Afterwards he discovers he became a sage at some point, beats the hero, but the hero is mind controlled?
Might be this one
Tsuihou no Kenja, Sekai wo Shiru ~Osanajimi Yuusha no Atsuryoku kara Nigete Jiyuu ni Natta Ore