The Detective is Already Dead.: The Lost Memory

I, Kimihiko Kimizuka, was an ordinary high school student. Sure, I had a penchant for getting dragged into all sorts of trouble, but was otherwise ordinary-until I met her. The detective, Siesta. Her angelically beautiful face and cool disposition in the face of plane hijackers swept me off my feet…and the next thing I knew, I’d spent the next three years off on a whirlwind adventure acting as her assistant. After all, I was the Watson to her Sherlock. But then…she died. It didn’t end there, though. No, our story only really began a year later when I met a bratty, snotty high school girl who seemed oddly familiar… (Source: Yen Press)

The story of Tantei wa mou, Shindeiru. follows Kimihiko Kimizuka, a young man who four years ago became the assistant of a mysterious detective known as "Siesta" on a hijacked airplane. Together, Kimihiko and Siesta went on mind-boggling, globe-trotting adventures while combatting a secret organization, but all of that came to an end when they were separated by Siesta's death. In the present day, Kimihiko tries to return to an ordinary, boring life as a high school student, but things are never that simple, even though the detective is already dead. (Source: Crunchyroll, edited)