Haha okay, yeah it is pretty hard for anime or manga to portray Seishin's monologuing. I think most of his characterization comes from those monologues rather than his actions, and he doesn't do a whole lot (compared to other characters). So have you read the entire novel then?

I'm actually starting to get kind of pissed off at the anime and manga for not following the novel more closely. I'm naturally biased towards the idea of "wah, no adaptation can be better than the original"...compared to the novel, the anime now seems kind of basic, putting Natsuno and Tohru and Megumi more into the spotlight than Ozaki or Seishin, the true protagonists of the novel, for the sake of fanservice. I have to remind myself that there was a reason I got into Shiki; Natsuno and Tohru and Megumi's roles are all still well done regardless, as is the creepy atmosphere and the OST. I'd still want to see a straight adaptation of the novel but I don't know how well that would go considering it's so long and has so many monologues and thoughts that might be lost in transition. It would need a lot of funding, maybe preparing for over 50 episodes...and then it would have to go very slowly too; it's hard enough to keep track of who's who even if you're reading the novel. And possible viewers would probably drop it because it's so slow, so in the end it would have to cater especially to novel fans, and there's not enough of us for them to profit from making such an anime.

Regarding who knows who better, I agree with the introvert/extrovert characterization, but also paradoxically I think that by revealing a lot, Ozaki reveals very little about himself. Ozaki complains and chats a lot, but it's about very superficial stuff; he's not very introspective. But that doesn't mean he hasn't got a personality. Often when people are feeling unhappy but don't want anybody to know something's wrong, they'll act cheerful and talk to things that aren't related to anything. So when Ozaki does talk, I imagine he'd rarely reveal his inner thoughts (He would say "My mother's such a nag, hahaha" even if he's feeling "My family's been oppressing me all my life, maybe if it wasn't for her I wouldn't have had to ruin Kyoko's life by marrying her and giving her a husband that doesn't love her, what kind of a man am I").

For instance, in the anime it's shown that Ozaki was somewhat intimidated by his father and didn't want to end up like him. If I'm not mistaken, he's alone at this time and it's never shown that Seishin even knows about those kinds of thoughts. We have yet to get to that part in the book, but perhaps it's just that he doesn't see his personal problems as important enough and pushes them aside (which is also kind of heartbreaking in a way).

Whereas although Seishin talks perhaps less, when he does talk it's more about morality and personal feelings, stuff that reveals his true feelings and beliefs about the world. Therefore, if the one he's talking to listens closely and perceptively, they can perceive a lot about Seishin as a person just by hearing his opinions on the world around him. Ozaki doesn't seem very perceptive, but then again he does have a sense of the emptiness inside Seishin and never lets him know that he knows. So I got the idea that Ozaki's hinted to be more perceptive than he seems. But then the reason that Seishin ends up being more understood by Sunako rather than by Ozaki is probably because after she figured out parts of his personality, she discussed it with him and helped him come to terms with himself, whereas Ozaki probably didn't think it was necessary to bring it up, or didn't feel comfortable entering into a conversation of that sort.

And since Seishin is more introspective and has thought a lot about human nature, there's no doubt that he understands 'people like Ozaki'--he kind of talks about it during the seme chapter (ie, everyone wants to be the center of everything) but that doesn't mean that he understands Ozaki himself. And finally, Seishin is constantly being surprised by Ozaki whereas Ozaki is never really surprised by Seishin. It seems like Seishin knows more about how Ozaki 'should be' and looks up to that, but fails to see who Ozaki really is.

I feel like Seishin will gradually start doing what he wants in the future, now that he's not being judged by God, and I think that'll actually make him happier. All his life, he's done what's expected of him and is also afraid of bringing down divine judgment on himself. He essentially won his own happiness at the end when he went after his own whim and spared Sunako, so I think there'll be more where that came from. Yeah, he's a great foil for Tatsumi; Tatsumi puts Sunako first, and Seishin finally learned to put himself first.

And I followed you! :D