The Dead and The Detective

Matsuda Jinpei was dead.
He'd been dead for a while now, in that explosion. And he quickly found out ghosts were real, he was a prime example. Ghosts aren't as simple as they seemed, apparently. The moment he was aware of his death, that he was a ghost, he got bound to someone.
The rules were simple, good people die, turn to ghosts, and get bound to someone as their guardian angel. If that someone turned out to have the guardian angel fate as well, died, then got bound to someone else, you go with them, get bound to the same person. It can go on for eternity, only stopping when someone you're guarding is bad. Some people have the Guardian fate without having a guardian themselves. They're called the Antarangs. Although they are rare, they exist. Like Jinpei's own Ex-Guardian & Ex-Best friend himself, Hagiwara Kenji. Kenji was the one to explain all that to him, apparently Anatrangs get that explained to them by the higher Angels. Guardians can whisper things to their Assigned, but only a litt bit, they can't talk freely.
Jinpei and Kenji expected to be assigned to Furuya Rei, their best friend and colleague next, and it made sense for them to be, he WAS a good guy and he had been their best friend.

So why in the ever-loving FUCK was their Assigned a random 14-year-old-genius they've never met before?!
(They did meet him before, he was much, much younger though, only being 9 years old at the time.)

Kudo Shinichi heard whispers all the time. He never understood where they came from, he never believed in ghosts so that was not a possibility, (He was starting to reconsider) he started hearing them when he was 14, yelling and cursing and flirting and crying. It was gut-churning, he always felt unknown presence around him, but they weren't bad, so it was fine.

(He ran, 16 years old in his 6-year-old body again, wondering where he went wrong, wondering why he hadn't listened to his Ghost friends.)