As I said in my reply to the above comment, I do see Kikuchi as being very Slytherin-ish: "There's something sort of clever and calculating about the way he figured out that it was the image of true love between Iwaki and Katou that appealed to the public, and also how to wreck that image. At the same time, it was kind of dumb, since it ended up getting him fired, but Draco and Snape also let anger and jealousy win out over common sense at times, so maybe it's still a Slytherin quality. ^_^" Or maybe that bit of self-destructive impulsiveness is a hint of Gryffindor-ness?

Onozuka is also a Slytherin; no question about it in my mind. He's incredibly calculating and manipulative. It seems pretty obvious in Book 8 that he coaxed Katou into going to the orgy party specifically so that he'd have some blackmail material to hold over him later. He manipulates and toys with the people around him, apparently for his own entertainment, as when he and Miyasaka "accidentally" reveal Katou's infidelity at the orgy party (but is it really accidental?), and when he arranges for Katou to see the picture of Iwaki on Miyasaka's cell phone. But sometimes his manipulation is altruistic, as when he arranges that very complicated scheme with Iwaki to reconcile Miyasaka and Katou.

At the same time, Onozuka seems to have a Hufflepuff-like sense of loyalty to the people that he cares about, namely Katou and Miyasaka. He's had the orgy party blackmail material for a long time, but he's never used it against Katou, except to cause a little mischief between Katou and Iwaki. After all, he could have sold the story to the tabloids for a hefty price, or tried to blackmail Katou into getting him a good part in one of his TV shows or movies. However, as red_day_dawning pointed out in the comments of my Onozuka story, Firsts, he does have a conscience. He has a certain sense of honor, and there are lines that he will not cross--although I'm not sure that anyone but him knows exactly where they lie. After the reconciliation between Katou and Miyasaka, Iwaki comes to the conclusion that Onozuka is a good guy who really cares about his friends, and although Iwaki's sense of judgment is not all that reliable (he also initially trusted Miyasaka, and still has no clue that Asano betrayed him), in this case, I believe that he's right.

Onozuka's Hufflepuff loyalty is most evident in his relationship with Miyasaka. In Book 10, he warns Miyasaka that he won't stand by him if he does "something bad" (obviously, assaulting Iwaki, although he doesn't come right out and say it). When Miysaka fails to heed his warning, he is obviously angry and hurt--in Book 11 he says that Miyasaka has betrayed him as well as Iwaki and Katou, since the threat of losing Onozuka's friendship wasn't enough to stop him from attempting to rape Iwaki. However, in spite of this betrayal, he still works to mend Miyasaka's and Katou's (and his own) friendship. It's a very deep kind of love and loyalty to stand by someone who's betrayed you in such a way.

I'm sort of veering off the House discussion now, but I'm having a hard time figuring out exactly why Onozuka is so loyal to Miyasaka, who quite frankly, takes him for granted and doesn't really seem to appreciate his efforts--or at least, he doesn't bother to express his appreciation. The only solid hint we get is when--I can't remember which book or chapter it's from, but Onozuka says something to Iwaki about how there are many people in the business like himself (scheming and manipulative, I assume), and that it's interesting to be around a naive guy like Miyasaka. I interpreted this in my Firsts fic as: "For someone like Onozuka, who was constantly scheming, Miyasaka's straightforward nature and predictability were comforting...He was also faithful, loyal, and dependable--kind of like a golden retriever, actually." For that second part, I'm taking a little artistic license and assuming that Miyasaka is a dependable friend, at least when he's not stalkerishly obsessed with Iwaki.

Okay, so back to the Sorting. I'm not sure what House Miyasaka is in. I sort of feel like he tries to be a Slytherin (trying to blackmail Iwaki into sleeping with him), but isn't really successful at it. His hotheaded impulsiveness strikes me as more of a Gryffindor, but on the other hand, trying to rape someone seems like more of a cowardly act--and even more cowardly, to try and put the blame for it on everyone but himself. On the other hand yet again, it wasn't really brave of the Marauders to gang up on Snape three or four to one, either. After reading the Onozuka and Miyasaka-related chapters many time over, I believe that he may have had good intentions with the rape attempt, in a rather sick and twisted way: he tells Onozuka that he won't be able to get over Iwaki unless he can make Iwaki hate him, and so he does something that he thinks will make Iwaki hate him. I think that in his own twisted little mind, he's trying to save his friendship with Katou by trying to stop his infatuation with Iwaki in the only way that he knows how. Of course he hasn't actually thought things through, and everything goes horribly wrong, and it's only thanks to Iwaki's forgiving nature and Onozuka's scheming that things turn out all right in the end.

And of course I can't ignore our heroes, Iwaki and Katou. Katou is definitely a Gryffindor in my mind: brave, well-meaning, and like his friend Miyasaka, hotheaded and impulsive. (Hmm, Onozuka seems to like this type of guy? ~_^)

I'm not so sure of Iwaki. Certainly he's brave and idealistic, but he's also thoughtful and reserved. Maybe more of a Ravenclaw? He's also loyal, sometimes to the point of blindness, as with Asano, so also a Hufflepuff in some ways. A combination of the three, perhaps, since people rarely fit neatly into one box--which is part of the problem of the Hogwarts Sorting system, but that's a topic for another essay in another fandom.

Kaneko and Shimizu: Hufflepuff, definitely. They're loyal to their clients, and hardworking and dependable.

Yoshizumi: I'm not really sure. Maybe a combination of Gryffindor and Hufflepuff? Risking his life to save the film during the fire was certainly an act of Gryffindor braveness--and possibly stupidity, although that's a bit harsh. (I can appreciate his dedication, but think of how devastated Katou and Iwaki would be if he sacrificed his life for a canister of film.) And he shows Hufflepuff loyalty in willingly stepping down and letting another actor take over his role for the sake of the movie.

Asano: the epitome of Slytherin-ness. A guy driven by ambition, who will do anything to get ahead. He seems to have changed slightly for the better by the time we meet him again on the Fuyu no Semi set, but I think he'll always be ambitious at heart, which is not necessarily a bad thing.

Mochimune: another Slytherin. Will use any means to get the ideal performance out of his actors, as Iwaki discovers. I don't have a good grasp of his character yet, but as snapelike said in the comments of Firsts, it would be interesting to see him go up against another Slytherin, such as Kikuchi.

As for other Youka Nitta characters...Shu Ti Fan of Casino Lily is certainly a Slytherin; I have to think a bit more about the other characters. As for Secret Diplomacy, both main characters are obviously Slytherins, willing to sacrifice their sister/wife for their own ambitions, which is why I can't like them, even though I'm usually partial to Slytherins. I'm only just starting Boku no Koe, so I can't comment on those characters yet, though I've heard that there's a Snupin-ish couple?

EDIT: I forgot to mention, it does take some courage for Miyasaka to face Iwaki and Katou at the barbecue after the way that he's betrayed them, even though they did forgive him. So I suppose I have to give him a little Gryffindor credit for that, even though I still think that they forgave him way too easily.