Waai! Omoshiroi!
I agree with the others who mentioned the Gosho Geniuses and their houses. Heiji would really fit the part of a true Gryffindor. Heck, I bet he can even pull Godric's sword from the Sorting Hat if the situation calls it (not to mention he's a kendo practitioner). Oh, OH! And is it a sin to say I can see him as a Quidditch beater for the Gryffs (Oh, or maybe even throw in a specific Quidditch team he supports?)? He probably enjoys Defence Against the Dark Arts class, as well as Astronomy, and a bit partial about Divination (try as he may deny it, he's probably not so skeptic about lucky charms and superstitions after all, thanks to Kazuha and her good luck charm). Also, I imagine him being a common sight in the infirmary, heheh. xD
Shinichi would most definitely be in Ravenclaw, for reasons pointed out by the others. I imagine the statue which gives the Ravenclaw students riddles to get into the common room (what's her name again? I've forgotten) being super annoyed with him, though, as he sometimes goes in and out of the common room just for the fun of it (the statue gives different riddles every time, right? heheh). Like Hermione, I imagine him being skeptical with Divination, but enjoys Care of Magical Creatures and Arithmancy. Despite being a capable musician, he's probably turned down invitations to join the school band (haha, scratch that last one, that's totally random xD)
Hakuba? Uhm... Probably Ravenclaw or Hufflepuff? I mean, he's smart and seems knowledgeable and he'd fit in either house just fine. Considering his obsession with time (and probably an inner desire to show off whenever he has the chance to), he'd probably even own a Time Turner some point in time and take every subject available. I see him as an outstanding Herbology student and, for some reasons, Charms specialist. He spends most of his alone time in the library... Oh, also, out of the four, he's the most probable one to become a Head Boy/Prefect.
As for Kaito, I see him as a resident troublemaker (ahem, cue the Weasley twins) but can't decide which house he'd fit in perfectly--Gryffindor or Hufflepuff? Either way, I see him enjoying Potions (heheh, in case he has to transform into someone or make someone fall in love, or if he needs a little 'dose of luck', lolwat?! i also imagine him being all buddy-buddy with Professor Slughorn, OH THAT WOULD BE A SIGHT! *hearts*) and Transfiguration (whoa! how does Animagus Kaito sound like to you guys? xD), and is a capable flyer (he can pass off as a seeker or a chaser). OH! And he's a loyal Weasley's Wizard Wheezes customer and a patron of Hogsmeade's The Three Broomsticks!~
Also, I imagine all four boys developing a love for the Ancient Runes, for some reasons. xP
As for the girls... Gryffindor (I can't imagine Kaito being in a different house as Aoko, though *sigh* me and my AoKaito tendencies...). Definitely Gryffindors (except Akako, who will probably land in Slytherin)
. I see Sera-san in Gryffindor (an Animagus, too, for some reasons), Haibara in Ravenclaw (a future Potions master, even), and Sonoko in either Gryffindor or Hufflepuff.
Oh, coincidentally, Makoto-san should rightfully be placed in Gryffindor...
Oh darn, did I say too much? You were only asking for the houses and this came out of the top of my head. gomen.
As for the Avatar AU... Uhm, honestly speaking, I find this kinda tough to think about...
Level-headed Shinichi would be a badass Waterbender, although a little part of me thinks he can also pass as an Airbender, but... Honestly speaking... a
bald Shinichi with arrow tattoos? Really?Putting the tattoos aside, Shinichi's calm and the philosophies he believes in doesn't come too far-off with the Air Nomads' non-violence pact... so yeah, I guess I'm sticking with an Airbender Shinichi for this one... Oh, and imagine him with a pet lemur? :"3
Heiji, on the other hand, completely opposes Shinichi's calm way of doing this and is usually easily angered and temperament, which will make him pass as either a Firebender or an Earthbender... Oh, no wait... LAVABENDER Heiji seems more likely.
Okay, so I'm sticking with an Earthbending/Lavabending Heiji on this one... But as a nonbender, Electricity-powered gloves or swordsman would fit him just fine. I see him with a Fire Ferret
(ugh, Pabu, I miss you!~) Hmmm, I don't see Hakuba as a bender at all, though, which makes me really sad coz I really wonder what kind of bender he could/would be. It's just that... he doesn't seem to be the type of guy to get into martial arts...
I imagine him owning a messenger hawk, though, or affording a dragon. So if we're talking about a bender Hakuba, he's probably going to be a Firebender... That, or a Waterbender with his calm and collected way of doing things. He'll make a fine Air Acolyte as well, actually.
Kaito will make
millions as a mover star! He's got an incredible charisma which is much different than the other three, probably even in an action film alluding to Lupin III (or is it just my fan girl heart speaking? haha XD). All jokes aside, though I see him as a Firebender with a lot of fuel in him (coincidentally, i just watched Kaito using his turbo-engine skates and thought, "hey, he can do that too with fire coming out of his fists!"). Oh, OH! If it's fire, it can also make an interesting back story about Toichi and that supposed 'fire accident' which caused his death... OH! And you can make it appear as Kaito concealing his Fire Nation origin and drawing out his father's killers as a mover star! ^_^
Plot B would be Kaito as an Airbender who lost his father from Firebenders in a staged accident and since knowing this has concealed his bender background and became a mover star to sniff out his dad's killers
(or does it sound too Avatar-ish cliche?). As for the girls, I see Ran as a badass Earth/Metalbender... That goes for Kazuha as well (no wait, I see her as an Earth/Sandbender, for some reasons). Sera-san would make an excellent Firebending spectacular combined with her Jeet Kun Do (so badass~). Haibara's more of a Waterbender who specializes in healing (as mentioned earlier by Crimson). I see Aoko as an Airbender, oddly enough, who, unlike the main gals, can read the wind and is smarter than anyone thought. As for Sonoko? Perhaps a non-bender and heiress to a big company. Akako would be Water/Bloodbender who has mastered her art and can control people any time she wishes (ooh, scary). That, or a Firebending Akako who can also bend lightning...?
Coincidentally, Makoto-san would make a capable Earth or Firebender (but judging by the way he utilized his surroundings more than twice, I'd say Earthbender). Whichever, he'd probably be into Pro-bending!!! ^_^
Uhm, was this post too long? *hides in embarrassment* :"3