How cool is the shinigami? We’re used to images of the Grim Reaper and Charon’s boatmen and so forth, but the addition of the skeletal wings and the black sugegasa really hits home the notion of these creatures as reapers of souls, gathering up lives like so much wheat or rice. If PCs abuse their raise dead and resurrection privileges, or otherwise disrupt the orderly progress of souls from life to the hereafter, you can bet they’ll run into one of these outsiders.
It’s interesting comparing shinigamis and psychopomps. Most likely your campaign only needs only one set of soul shepherds or the other. But if your campaign includes both, as Golarion does, one wonders how the two groups get along and share jurisdiction. Given shinigamis’ comparative strength and lawful nature, maybe they are contract employees or bounty hunters, brought in to hunt down particularly troublesome souls or relieve overworked or outclassed psychopomps. On the other hand, being lawful, shinigamis might be more likely to broker and honor deals with mortals (any system of law involves loopholes and appeals processes); certainly they have more of a reputation for going rogue than their inscrutable and aloof neutral counterparts.
Also note that in Japanese myths sometimes shinigamis tempt mortals to suicide. So while most shinigamis will not take a life before its time, they’re not opposed to convincing mortals to hurry the journey along…
A morrigna (see Pathfinder Adventure Path #48: Shadows of Gallowspire) hires adventurers to dispose of a shinigami—the outsider has so far eluded her, and she recognizes that should they come to blows the she may well lose one-on-one. If the adventurers find the shinigami and parley rather than fight, they discover its many death warrants appear to all be in order. So who is lying—the morrigna or the shinigami? Or is there a third player involved/
After overzealous use of resurrection, a shinigami comes looking to collect an adventurer’s soul. The shinigami is unfailingly polite but determined, using deadly force against the other members of the party if necessary. There is one deal the shinigami’s victim may strike with it, however. An asura has been diverting atheist souls meant for the Faithless Quarter. Disrupt the asura’s plans and the scofflaw adventurer will earn a reprieve.
Adventurers are spending an evening in a bayou bar on one of the more dismal planes when they come across a disturbing exchange taking place in the corner—a shinigami and a thanadaemon trading soul gems. Overzealous eavesdropping will surely alert the pair (the shinigami has Perception +31) and they take a dim and very violent view of any mortal observing their transaction.
—Pathfinder Bestiary 3 244
Edit: Apologies for the lateness of this post. Original entry: Hey guys, too sick to post tonight, and I want to do a good job because the shinigami is really cool and I want to do it justice. Bear with me for 24 hours [or 9 months—sorry AlgaeNymph!]. Thanks!