Yuusha Party ni Kawaii Ko ga Ita no de, Kokuhaku Shitemita.

Youki died in a traffic accident and was reborn in a fantasy world! However, instead of being the hero of legends, he ended up reincarnating into an overpowered demon. Having no desires to become the Demon Lord, he sits around in the Demon Lord's castle as a random low rank guardian. One day, the Hero's party comes to attack and on a whim he knocks...