Suisei

Youki was reincarnated in another world. However, instead of being reincarnated as the hero or the demon lord, he was instead reincarnated half-assedly as a minion of the Demon Lord. One day, the Hero's Party attacked the Demon Lord's castle with the intent of defeating the Demon Lord. Of course, Youki was able to repel their attempt with ease. In spite of this, he ended up falling for the cleric, Cecilia, at first sight...