GuessAnime.

Kai, who comes from a family that specialized in dark-style occupations, sought even greater strength.One day, he saved the fourth royal princess who was under attack by monsters. This was the the trigger for him managing to join an academy that specializes in training people for holy occupations.He endures training so incompatible with his physical constitution that it could make him faint, all to become the polar opposite of the strongest dark knight—the Kingdom's strongest holy royal knight, The Royal Paladin.An occupation-change drama of a genuine dark knight begins!!"Now let us enjoy our deathmatch—to our hearts' content"

I'm a Dark Knight But I Aim to Be the Strongest Holy Knight is finished and has 15 Volumes and 75 Chapters. It is also Known as: 暗黒騎士の俺ですが最強の聖騎士をめざします, I'm a Dark Knight, Yet Aim to be the Strongest Holy Knight., 暗黒騎士の俺ですが最強の聖騎士〈パラディン〉をめざします, Ankoku Kishi no Ore desu Ga Saikyou no Paladin wo Mezashimasu

Genres: Action, Adventure, Comedy, Fantasy, School Life