^
Right. Okie. Good for you..
I recall you mentioning how bad it was for you to recall info for school in one of your threads. For a class you weren't familiar with, right? In your Xian college, right? Fascinating and all, but it was hard to shove through all the info, right? And you tried your best to memorize but it was too hard !_!
So, how's your Si, hmm?
Even if yours is decent, or good, Light's memory was insane. From the get go. Insane-- And what of your recalling of
massive amounts of details?

And of people? (people would be easier, but perhaps exact names/faces might be a bit hard unless learned over time to better it). And you may have that ruthless drive, but would you think you should and COULD be In Control of the whole world, even at that point? That you are the ONLY one capable of doing it? He didn't just want to rid the world of evil or scum, he wanted to Rule It.
Also, what we know of him before he turned, he wasn't so social at all to begin with (right people? err). He just did his duty, did as was asked/required, and called it a night. It's just that it eventually became boring for him. Even if popular with girls, as was implied, he didn't encourage it. He was good looking, but used them as he needed them. And kept them in his pocket just for that, as he did later on.
Kiddo, I see ISTJ as well... my dad's one... his memory... @_@ He just recalls things easily. Drive to a new place? He'll recall every stop, every sign....w/o having to say it, he'll just know how to go back after years of not going. And he has no qualms with invading one's space to "inspect". Today, I just found out that he has a spare key to my bedroom lock, to which he opened it with while I slept last night, and I'm taking it back -_- Even though he's not outgoing, much, he is a charmer with others when he is out and chooses to be or chooses to be quiet. Or on the phone with friends, he'll control the conversation. Turns the phone off and right back to silence or reading/watching/eating or w/e. And he keeps up with all sorts of news, through the TV, newspaper, Internet. He just reads and reads @_@ and just doesn't forget.. Pedantic, also, but nevermind that.. He likes to know about grades, will talk to teachers as it's expected, etc. He likes to control everything, if it applies to him or his family zz (but I've helped him get over that over the years...at least, with regards to me..mostly ^_^'')
Freaky @_@
ISTJs will not stop once they have a cause. Will stop at no lengths.. and they can work for a long period of time as well... They also won't become emotional when confronted. INFJs, while cool or calm, I wouldn't think would exert such control in a similar situation. As messed up as he was, I'd see him giving himself away much sooner than he did if he were an INFJ.
He wasn't really idealistic to begin with, though. The whole "world is doomed" view. Only thing that changed that was the Notebook. It became more than a Muse.. to slate his boredom with and then his vision which was NEW. He never thought of doing it before then-- Once given the tool, he thought about it. If he were an INFJ, he'd probably have thought about it a long, long time ago, especially when confronted with his dad's work all the time or helping out. The "What if (I could change the world/I could help/etc)?" never occurred to him until then. If wrong about that last bit, correct me, my memory is fuzzy now qq
AvereX, I can't see him as INTJ. Same issue with INFJs with Dom Ni, except they'd be better with recalling logical details, however they won't recall it the same way an ISTJ would... same issue with crazy memory not being available to INTJs, initally or unless they learn to. And if I recall correctly, they aren't so keep on recalling details/facts as much as an ISTJ would. Dom Ni and all, it's all future oriented, and having Demonic Si...well... it's our weakest function @_@... so unless we learn, it won't develop as well. And I doubt that it'd develop that well as Light's unless we were put into a situation early on to nurture it. Light's life/situation was bland and boring, as well he just naturally had it. He was also a great speaker and had excellent communication skills, even so far as to be casual or come up with something on the spot. INTJs, while great with Te, might not be so when dealing with casual conversation (just for the hell of it, or won't even bother to, let's be serious... Why bother?! What's the point?

They can further their cause w/o that BS, unless desperate, but they can be stubborn about that...).
I'm sure someone mentioned ENTJ, either here or elsewhere. That's possible too. Maybe even more so than ISTJ? err Did anyone say that Yagami Sr was an ISTJ also?