The Detective Is Already Dead, Vol. 1

"You will be my assistant."
During a plane hijacking four years ago, Kimitsuka Kimihiko wound up becoming the
assistant to a beautiful detective named Siesta. The pair traveled the world, solving
crimes and battling criminal organizations. Until Siesta died, anyway. Kimitsuka
thought that would spell the end of his adventures and a return to ordinary life, but
an encounter with a girl who bears an uncanny resemblance to Siesta suggests that
fate has other plans.