I'm Going to Battle Some Assassins

I Was Reincarnated as the 7th Prince so I Can Take My Time Perfecting My Magical Ability

The kingdom has been infiltrated by a girl named Ren from the Assassin's Guild. Upon learning of her special ability as the Poison Blighted, Lloyd tracks her back to her hideout, sneaks in, and is attacked by a group of assassins with unique abilities.