1 Going under the spoiler tag It may be significant that Hiroshi does not appear in the OP, but a much taller blond guy does. It's a brief appearance, and in such a manner as to suggest he is an opponent, not ally.  So... either Hiroshi is the bad guy under shape-changing magic, or it's his older brother, and Hiroshi is just an extraordinarily gifted liar and agent provocateur.   For the moment, Fujiko is Sai's direct foil, and is an "evil girl" -- but I think she's the red herring we're supposed to suspect.   It hasn't captured my attention the way Railgun did, but I'm really liking this show, and have re-watched episodes 2 and 3 a couple of times. It's fun in a an almost-but-not-quite-out-of-control way, thanks to good pacing.

Another thing: since its origin is a light novel I'm suspecting that several pieces are going to fit together at the end, such as the lecture about mana, the fate of Fujiko's older brother, Keina's bird, and the war from 100 years ago.  Also, everyone is assuming that Sai, as demon king, would bring a reign of terror.  He could also be a benign king that keeps other demons in check--and the difference in his destiny may lie in the girls, of course.

2

He has tremendous power, and the clear destiny of developing far more. But he also clearly has free will and the ability to choose what he'll do with that power.

Part of why I expect what I said is that it fits with the kind of story telling I'm seeing, which is to say that it's uninspired and formulaic. "Hiding in plain sight" is the standard way of doing this.

3 On the other hand, it's far better than waiting until episode 10 to introduce the big bad, like too many manga-based anime do. 

One of the things I'm liking about this show is that the feel also hearkens back to Maburaho, in that we have an entire school of magical teens, and magic is everywhere -- though it developed the secondary characters better for the first few episodes, I think.   Before it turned into dreck, that is.

4

For me the real mystery is Kena.

Is she a ditz, or is she crazy like a fox? When Korone revealed the truth about the drug, Kena didn't seem surprised or shocked. Did she already know? Did she redirect the drug deliberately to foil Fujiko?

Sai himself wondered about that. But it'll take time to find out. The other possibility is that Kena really did think it was a friendship drug, and expected it to make everyone stop fighting. And as to why she wasn't shocked, maybe she's too silly. Or maybe it was an act.

If we're looking for another illuminati, maybe she's it. Junko is thought to be the leader of the good team, but maybe it's really Kena.

Maybe she's really powerful and capable. Why wasn't she even slightly harmed when Sai let loose his nuke in ep 2? She was right there at ground zero, and ended up at the bottom of that crater, yet her clothes weren't even slightly singed. Junko, on the other hand, was down and needed healing by Korone. Maybe Kena didn't get hurt because she was able to protect herself. (If so, she would be the only one around strong enough to do so.)

Korone knows things, and Korone actively cooperates with Kena and follows her orders. Why would Korone do that?

Like Hiroshi, maybe Kena is playing a part. Maybe what we're really seeing  is a big chess game between Kena and Hiroshi, each trying to recruit Sai for their respective teams. He's the prize; whichever team gets him pretty much wins... whatever it is they're competing for.

I don't think that Kena is the "childhood friend" who is herself in love with Sai. Reason is, she's trying to set Sai up with Junko. If she were the stereotyped "childhood friend" then she'd be just as jealous of Junko as of Fujiko, but she doesn't seem to be jealous at all, of anyone. To the extent that she's foiling Fujiko's plans, it doesn't seem to be romantically motivated.

But like Hiroshi, she seems to be hiding in plain sight. Her actions are clear but she's hiding her motivation and seeming to be inconsequential. And like Hiroshi she's manipulating Sai, in subtle ways.

I won't be at all surprised if it turns out that she's the other leader.

5

A bit more about Kena: Her entrance line in ep 3 was, "Maybe you can't change who someone is, but you can change what they think."

The point being that she's telling Junko that the plan is to try to recruit Sai for the good team, rather than to kill him in order to deny him to the bad team.

If so, then that explains Junko's sudden change of heart. She just received her orders, and is obeying them.

6 So, was it Junko's rapid change of heart a plot point, or just lousy writing? I hate it when I have to consider that question.

7 My money's on Keina (that's the spelling in the subs I'm downloading) being a the ditz.

No harm?  Stupid is invulnerable. (I was sure that was a trope)
Says odd things that make people go "waitaminute, that makes sense.."  Genius Ditz.

I might have come up with more, but I got lost in TvTropes again..

Anyway, I think you're desperately trying to find meaning behind meaningless things. There is no method here....more importantly Why the hell did Korone fire the rice gun at Sai, Keina, and Junko? Is that what Keina told her to do, thinking the medicine was what Fujiko claimed it was?  In that case, why didn't Korone check the medicine before firing it?  Did she not know about it?  At best this would imply that Keina is not all-knowing or even very bright, since she was setting herself up to be a slave to Fujiko.

8

Or... she knew Sai would stop it. Just as the bad guys used the attack in the barracks to get Sai to be cruel and evil with his power, the rice attack made Sai create a shield around him, Kena, and Junko.

If you notice, when Korone fires it, Kena doesn't look worried. (Of course, you could argue she's too stupid to be worried, but I think it's just as likely that she had other reasons for not being worried.)

A few more episodes will tell. But you are right that I'm trying to make this into a decently told story. As I mentioned above, these things could be plot points but they could also just be incompetent story telling.