Tantei wa Mou, Shindeiru.

Kimihiko Kimizuka calls himself a trouble magnet, so being kidnapped onto a hijacked airplane barely feels out of character for his life. There he meets Siesta, a legendary silver-haired detective who resolves the crisis and then recruits him as her assistant despite his objections. The two spend three years pursuing crimes and organizations capable of threatening the world, until Siesta suddenly dies and Kimihiko tries to bury that life with her. A year later, a new girl enters his life with a case that seems unrelated, but every clue begins pointing back toward his dead partner. The detective's death may have ended their travels together, yet it clearly did not end the investigation, or Kimihiko's role in it.