only know three of the 4 greater (high ranking) noble houses so far, Kuchiki, Shihōin, Jūshirō. don't know the 4th and there used to be 5.

any idea why they fell

It hasn't been stated yet. I actually think it has something to do with Isshin because I think he is part of the Shiba clan. My reasoning for this is simply because Ichigo and Kaien look so similar. I might be wrong though.

Now there's a possibility that I hadn't thought of. Hmm.

I was thinking that Isshin might be ex-Royal Guard. That would explain his whoop-ass reiatsu (its mentioned in chapter 187 or thereabouts) and captain's insignia, since all of the Royal Guard are promoted Captains. Isshin being promoted far back enough in the past might explain why the name "Kurosaki" never raised any eyebrows when Ichigo first went to the Soul Society, as supposedly only other Captains know about peeps getting promoted to RG. The time-line here gets a bit funny though, because Urahara mentions that its only been 20 year since Isshin's shinigami powers disappeared/whatever. But! The Royal Guard operates in mystery and completely independent of Gotei 13. So if Isshin had to leave the RG for some reason it wouldn't be a surprise that none of the lower-downs in the Gotei 13 didn't know about it. That, and this would be a prrrfect opportunity to tie in the whole vague RG/Soul King/Ouken thing in with the current situation. That's my theory.

'Course, now that I've spent 15 minutes typing all of that watch it turn out to not be the case. Oh well: doujinshi.

(As for Masaki, I'm pretty convinced that she was a Hollow. If that ends up being the case, then Bleach is set for a serious case of Shoujo romancicitis, the Forbidden kind. I do not think that this would be a bad thing. Not at all. )

I actually think that Masaki was the old 12th Squad Captain. It would explain how Isshin and her met, if of course Isshin was part of the Royal Guard as well.

Oh, thanks. Too much D&D.

Oooooh I like that idea too! I love that nobody has a clue. Something exciting and new is happening in Bleach!

Of course its all contingent on what Aizen meant to say when he was saying "You are a shinigami and a- " before being so awesomenessously cut off. (Well...duh, Noisette, that's why its cliffhanger.)

I'm leaning towards Masaki being a Hollow because it explains why Ichigo is so "special" and why Aizen, who is interested in making Shinigami-Hollow hybrids, would be manipulating Ichigo's fate since the day he was born. Imagine what a damn stroke of luck it must have been for Aizen to find a naturally occurring hybrid. He clearing hasn't been too impressed with his "synthetic" hybrid Visoreds and Arrancars, even if both experiments proved to be far more powerful than regular Shinigami and Hollows. But Ichigo is the real thing (which would also explain why he is so insanely more powerful than everyone else). By throwing all of this crap at Ichigo he can observe how a real hybrid would fair and grow under various conditions. And with that information Aizen can do...whatever it is he plans to do with that information. Get himself an Ouken. Rule the universe. Go to Tokyo Disneyland.

Of course there are holes in the Masaki-Was-A-Hollow Theory. For instance, how could she run around as a human if she's a Hollow? Ah, but, if Isshin knows Urahara - who makes all kinds of improbable and convenient things - perhaps he could have made her a Hollow-friendly gigai? I guess I have a whole week to plug those holes with shoujo-inspired conjecture.