Yuusha ni Minna Netoraretakedo Akiramezu ni Tatakao. Kitto Saigo wa Ore ga Katsu.

Alternative

勇者にみんな寝取られたけど諦めずに戦おう。きっと最後は俺が勝つ。; Even Though the Hero Stole Everyone from Me, I won't Give Up, I'll Keep Fighting. I'm Sure I'll Be the One Who Wins in the End.