The Detective Is Already Dead, Vol. 1 (manga)

The only surivor, me, and the detective's dying wish: their unfinished story.
I, an ordinary highschool student, Kimihiko Kimizuka,
I was embroiled completely flawlessly into a plane hijacking,
Where I became the assistant to the angelically beautiful detective girl I met.
In three years, the great detective and her assistant unfolded a dazzling adventure
dram--
Before long, we were seperated by death.
This takes place a year after that.
The only survivor, me, and the detective's dying wish--