YuYu Hakusho, Vol. 5 by Yoshihiro Togashi

[Viz] A delinquent’s gotta do what he’s gotta do…in the afterlife. Yusuke Urameshi was a tough teen delinquent until one selfless act changed his life...by ending it. When he died saving a little kid from a speeding car, the afterlife didn't know what to do with him, so it gave him a second chance at life. Now, Yusuke is a ghost with a mission, performing good deeds at the behest of Botan, the ferrywoman of the River Styx, and Koenma, the pacifier-sucking judge of the dead. Yusuke Urameshi was just another street punk until he died in an unexpected act of self-sacrifice...and came back. Now he's the Underworld's official supernatural detective, charged with keeping the peace between the mortal and immortal realms. That peace has been shattered. A gang of demons called the Four Beasts is infecting humanity with a swarm of nasty supernatural brain bugs. The only way to control the bugs is with an enchanted whistle...and the only way to the whistle is straight through the Four