Hmm, my theories:
Shiro's identity:
Given that he had a "flashback" to the Silver and Gold Kings, he probably knows them... My bet is on a split personality/manipulated memories/trauma induced amnesia.
Villains:
Well, Adolf K. Weissmann might as well be called Mr. Villain and I think he is a villain, but not necessarily the final boss. Still, he has an episode named after him so he's going to be pretty important. and probably related to Shiro. (Brother? Father? He could be both...)
And while Septer 4 don't look like bad guys, there's that mysterious connection between Reishi and the Gold King. Of course the Gold King may not be a bad guy at all... Anyway, I hope Reishi and Mikoto will be more concerned about having a glorious, manly rivalry as befitting two manly men with blue & red themes...
Also, Saruhiko looks suspicious. Maybe he's be a low-level villain, or just has some Issue that he needs to get over. (See more below.)
Blood relations:
As I wrote above, I wouldn't be surprised if Weissmann and Shiro turned out to be related. (
Weissmann... Ya
shiro... white-white...)
And for now my theory is that Reishi and Saruhiko are brothers. Seriously, two dark-haired glasses-wearing pretty boys with similar hairstyles and similar personalities
in the same organization? This can't be a coincidence... (oh yes, give me the delicious brotherly angst, mmm yeah)
Misc:
Why does Yata Misaki have such a girly name? (It has the kanji "beautiful bloom" which is decidedly feminine) Maybe he's really... a girl? Fukuyama Jun already voices a trap in Ixion Saga DT, why not a reverse trap? xD