Interesting, I feel like his cheeky manipulative side wasn't really hidden much ... I felt like the only time he acted calm and nice was more for his host persona, which I guess can qualify as a split personality if you want :3
In my opinion, Kyoya has less of a split personality and more of a really hard front, given his background of having to gain his worth through achievement. It's pretty well implied that he really does care about those around him, and just covers it up. His manipulative side seems to me to be more for comedic effect than for him being just an actually terrible person (though, to speak comedically, he kind of is a terrible person )
Hmm, answering the question ... Pretty much every Ace Attorney character ever