Oceanus Christum is a Gyojin trained in serveral martial arts and Swordmastering. After hard trainings he decided to join the Marine, where he was able to rank up pretty quickly, achieving the Vice-Almirant Rank in just two years. He was named with two different nicknames, the first one was Kuroi Mizu (黒い水, Black Water) given by his Gyojin comrades due to his use of Gyojin Karate and Busoshoku Haki. The second one, instead, was Akuma Hanta (悪魔ハンター, Demon Hunter) given by the Marine because of his abilities where he is practically perfect for hunting down Akuma no Mi users.