Descendants of Darkness - Season 1 Episode 7 The King of Swords (1)

A request from the Count himself leads Tsuzuki and Hisoka to the Queen Camellia cruise ship to investigate its ties with the mysterious longevity of a number of people who were due to die. Once on board, Hisoka finds himself drawn to Princess Tsubaki, the daughter of the ship's owner, while Tsuzuki is horrified to discover an old accquaintance alive and well. As one of the passengers is killed, suspicions turn to all directions but Tsuzki and Hisoka have one particular suspect at the top of their list.