I agree with that. Shuya is so ENFP, it hurts haha.
Fuckin lol'd
The thing with Kawada is that during the game, he seems INTJ, but in his flashbacks with Keiko in the manga, he looks like the typical ISTP.
Fascinating character. This will be a bit long...
I see what you mean. He does have that ISTP smugness going on about him after all (what with the cigarette smoking and shit. Ahaha). Just that, I really don't think he prefers Ti at all. Come to think of it, his practicality and canned knowledge about things strongly suggest ISTJ in my mind. I guess what really made me think of him as an INTJ was the whole...er, "masterminding" thing... I'm not convinced little bits of ISTP improvisation would've led to the shocking moment near the end, the revelation of his little plan (you know what I'm talking about, hehe let's not spoil it for the others)--it seemed more like the plan was formed when he decided to help Shuya and Noriko survive, and he stuck with it.
Besides, he seemed to understand Shuya whenever the little bugger would start throwing fits, and even though he always tried to act tough and clear-headed about things, you can see he's also emotionally affected with the fucked-up happenings (one awesome INTJ talent is appearing intensely courageous in the face of things that make them want to piss their pants...). Maybe the incident with Keiko has bolstered his Fi preference, and I think that's pretty obvious when he decided to protect the two people who were more a burden to him than help. He's got a great deal of insight into the characters of Shuya and Noriko, and it's not like he learned to trust them. He just knew he could. He decided their lives were worth saving. And I won't forget his explicit instructions about the two main players of the game: both were to be shot on sight, but Mitsuko would be a mercy kill, and Kiriyama you just shoot like a wild animal (I have INTJ friends who analyze and talk about their interpersonal adversaries in that wise. Haha). There's a lot of Fi and a lot of Te going on with Kawada.
There's also a thing about Ni-doms... appearing older and wiser than they really are. The gap between the ages of Shuya and Kawada may just be a year or two, but put them together, observe them for a bit and it becomes easy enough to spot who's the child and who's the adult, regardless of physical appearances.

One last thing... about the collar. I seriously doubt an ISTP would even know how to start messing around with that. But an INTJ, with his unique mind and strong intuitive intelligence... the only other type I can think of that could possibly mess around with it unscathed is INTP. Possibly. And doubtless you'll agree that Kawada's no INTP.
I typed him as INTJ at first, but I agree with you. Kiriyama definitely doesn't use Te. I would say INTP then, altough he is really hard to type because of his brain condition. I would have to reread the book to see if he uses more Ne or Ni.
This will be a bit long as well.
I think you'd find my main reasons for seeing the Kiriyama in the manga as an INFJ interesting... perhaps. For one, yes, he's definitely an introverted thinker. Come to think of it, in the beginning, it seemed that all of his other preferences were extremely overshadowed by introverted thinking, but as the game progressed I found that it was not so. I had the idea that the reason he's so adept at mastering things quickly were in part due to a highly evolved Ni, as well as excellent mimicry courtesy of a well-developed Se. And since his brain condition had something to do with blocking his emotions, he didn't give a shit about the world or how people around him felt. Hypothetically, an INFJ unable to realize Fe due to brain damage would have no interest in external judging, and thus would appear very much "perceiving". I'd go so far as to say that his cock-blocked Fe only manifested itself in minute ways, such as making an impression with dressing sharp, being elegant and stuff. Maybe subconsciously actually liked the hairstyle forced upon him by one of his pet uglies.

Actually, the real reasons for my assumptions are rather shallow.
1. Early in the Sugimura-Kiriyama fight, Hiroki claimed that Kiriyama seemed to "project Ki from within"... as if by magic. And, well, we uh, we all know INFJs are Magic People.

2. And did you see the way the guy moved...? HIS FUCKING SCHOOL JACKET WAS JUST FLOATING ABOVE HIM NO MATTER WHAT, WHAT THE FUCK MAN

That there is trademark INFJ grace! Only Magic People move like that!
3. Near the end of the story, Kazuo recalled that fateful incident from his childhood. He called it "The Bad Thing! The Bad Thing!" If that's not the introverted intuition way of a child defining a life-altering phenomenon, then I don't know what is. It led me to think that Kazuo Kiriyama must've had a developing Ni at that point of his childhood... then BAM,

I AM SUDDENLY ROBOTIC AND WITHOUT EMOTION. (check out the series of panels depicting his childhood before the incident, and you'll see that he was a pretty cheerful lad, smiling a lot, enjoying people, emulating his TV superheroes...quite unlike how I imagine the quiet and curious Ti-dominant child to be.) I suppose young Kiriyama was on his way to a cognitive development on the INFJ path before "The Bad Thing!" fucked around with his brains.
Again, this is just what I think about the Kiriyama in the manga. The Kiriyama in the novel was likely INTP. The Movie Kiriyama was more of a DICK.
The way he reacted to Takako telling him how she felt about him while she was dying made me think he was a Fi-user, instead of Fe-user. Maybe I don't understand Fe well enough, but wouldn't an INFJ would have known exactly what to say to Takako to make her feel better during her last moments? If I remember correctly, Sugimura was all awkward and didn't really know what to say.
Ah, you're totally right. The only reason I got the idea that he may be INFJ was that during the fight, he was struggling to "catch the moment". I guess I attributed that to difficulties with inferior Se. Yeah, Hiroki was definitely INFP.
What about Shinji Mimura? I always saw the three versions to be very healthy ENTPs.

SHIT I LOVE BR