Okay, as I'm not sure how much people know/understand about BLEACH canon, I'll try to explain things as best I can.
Ishida is rather good at sensing a person's reiatsu, the pressure one's reiryku (the amount of energy a person has) exerts on their environment. To give you an idea, he knew that Ichigo could see ghosts and when he became a Shinigami. He also knew of Kuchiki Rukia's true identity as a Shinigami and could sense the Hollows not only before they could, but even before Rukia's soul pager went off.
So my question to you, my lovely fellow players, is... would Ishida be able to sense your characters if say, for instance, your world has something that could be considered equivalent to the BLEACH idea of reiatsu/spiritual pressure? (To give an example of how we did this in another game, the Sonic the Hedgehog series has the Chaos abilities. We agreed that it might be similar enough to ping Ishida's radar. Not that that this has to happen here, of course, but you get the idea.)
He won't know who is who until he actually hangs out with them and gets to know them, of course and only if you want him too, but I figure it's something to play with and could lead to some CR later. Or something.
And saying no is okay too! Like I said, it's just something to play around with if anyone wants to.