Mata Korosarete Shimatta no desu ne, Tantei-sama

Sakuya Otsuki, son of a famous detective, set out to solve mysteries along with his assistant, Lilithea. But a strange thing happened with detectives: they became the victims of the crimes they investigated. On a luxury cruise ship mission, he finds himself murdered once again, and when he wakes up, he finds Lilithea by his side to help him solve this mystery.