I mean, he's polite and genteel and sweet and otherwise not terribly noticeable (except to his fans) because he's EXPECTED to be- but at the same time you hear (more than once, I think, but it might just be the one time) that it seems like no one could be that nice all the time, and that it seems like there's something missing from him (paraphrasing here, don't kill me anyone), so the expectation for any part of himself he might show after being told that would be a less pleasant, more commanding, MUCH less distant one. In other words, he's using people's expectations of him to invent both 'different personalities'- one polite and un-invasive and easy to ignore, the other harsh and conniving and uncomfortably intimate. I suspect what he's really like is somewhere between the two (though I always seem to assume a little closer to his 'dark side', because it's more fun that way XD), and that he uses his 'other sides' as a crutch to avoid having to be close to people and/or hurt/criticized by them, because in both cases his personalities are people you wouldn't necessarily be close to, just to different extremes (also, just look at his family- wouldn't you want to avoid critique to the point of constant hiding after growing up under that psycho grandma?).

Your analysis makes sense. People tend to compartmentalize themselves (I am guilty of this) and whether or not Yunoki has created his Dark and Light sides consciously or unconsciously, it seems that he has done just this.

See, there are prevailing expectations in society as per certain kinds of people, and Yunoki has been taught to mold himself to fit society's view. He is internally conflicted with his image of 'perfection', and I'm sure that's a hard thing to keep up. Perhaps, to offset such 'perfection' he has subconsciously created a demonic persona -- after all, not everyone has the looks of Adonis and the temperament of Athena, no?

I also suspect in 'reality' he is more of a cross between the two. He could also be shoving all his anger, fear, and 'bad' feelings into a little box in the back of his head and his random swaps in personality are because of this. ^^

I think you're both right- and to be honest with you, I do keep seeing that Yunoki is more truly good than similar to his darker, more manipulative façade. But he seems to have convinced even himself on such a deep level that he's not good- or not worthy of being good, who knows (and this is speaking as someone who's read some of the manga and watched the show, and never played the game- I'm mostly basing this off how I imagine he grew up in that family of his)- that he seems suspicious of his own actions. As if when he acts really honestly kind (like 'rewarding' Hino with his flute piece in the garden at the end of the first season), he might be tricking someone without realizing it, so he acts bluntly offensive to keep from getting confused about himself and then layers on top of THAT his distant gentlemanly face- it's no wonder he would seem so superficial when he's being nice.

Yunoki does indeed show signs of being confused about his own self-image. I perceive him as having suppressed fears, doubts, and maybe even wishing to be loved for who he is -- however, over the years he has build up so much of a façade that he is afraid to show weakness, such as emotion.

Perhaps in his family the "masculine" traits of lack of emotion, impassivity, and even subtle dominance were valued. I always thought that his harem was kind of creepy... O_o' I might be going too deep but it seemed to me as if he enjoyed and yet was inertly uncomfortable with being objectified in that way.

See, we can't really see Yunoki in two parts, Light and Dark -- not exactly; we'd have to look at him as a human being. Maybe he's stuck in between how he has been taught to build up an outer persona of perfection versus how he views himself, how society perceives him, and how the people closest to him perceive him also. It would be hard if even your friends didn't know the 'real' you. ^^