Now that I've actually watched Shingu I've been going back and reading commentary on it that I skipped over before in order to avoid spoilers, and of course I have some reactions to various bits of it. There are spoilers here, along with possibly too many words.

First, somewhere I remember reading a comment that it's vaguely odd that all of the aliens are either shapeshifters or more or less human looking. My answer is that we're seeing a self-selected subset of the aliens; we basically only see them on Earth and in order to be on Earth you have to be able to pass for human. Aliens that are clearly alien just don't get to come by.

(It's possible that at one point we see clearly non-human aliens, if they're aliens instead of robots. They are not trying to hang out discreetly on Earth, to put it one way.)

Author:

One plot move became more dubious with the second take: when Moriyama carried out Harumi's body out of the closed-off space, he should've not had the ability to do so.

I cautiously disagree. Harumi needs the paper Shingu to enter the closed off space (and then rips it up to trap her opponent in the space no matter what happens in the fight), but she is not a Chosen; it's possible that Chosen can enter and leave closed space without assistance. Certainly Moriyama enters the closed off space without a paper Shingu when he goes in after her.

So why did Harumi need and use the paper Shingu when she took Moriyama there, if he can get in (with company) unassisted? Precisely because she was taking him there; he did not know where it was and did not even know it was there.

SDB:

The one contrivance in the series is that at the very end of the first episode, Harumi finds out what's going on and runs to get help to stop the fight [between Muryou and Moriguchi, where they use their powers]. She doesn't run to one of the teachers who are in on the secret. She doesn't run to Hachiyo. She ends up running to Hajime, and she asks him to stop it.

In a comment on SDB's entry, pflorian advances the theory that Harumi went to Hajime because he's an outsider that Moriguchi would restrain himself in front of. I can believe this (and Harumi does specifically ask Hajime to stop Moriguchi), but I kind of agree with SDB; the more I think about this scene, the less straightforward it looks and the less entirely satisfying I find pflorian's theory.

The short version of why is that in order to make pflorian's theory work, I think that you need to make a series of assumptions that boil down to Harumi not really expecting Moriguchi to use his powers. You can make this make sense (there's a plausible way that Harumi could be ignorant of who Muryou was and why Moriguchi was so grumpy about him), but it requires some stretching.

(My chain of logic for this is that pulling Hajime in to restrain the fight only works if he's going to be close to the fight, like, say, on the same roof as the other two, and this is only likely if the fight stays on the roof of the classroom building, and that is only likely if Moriguchi does not plan on using powers. That Hajime is adventurous enough to cross to the gym roof clearly surprises Harumi, and I think that the classroom building's roof is clearly not a smart place for Moriguchi to fight with powers; it's simply too close to too many people.)

It's a great scene if you don't wind up thinking too hard about it, though. It plays out just like it should, using the classic patterns of its trope extremely well to pull us and Hajime along at a breakneck pace; from the moment Harumi goes 'please', it doesn't give us a chance to stop for breath. Since I was rewatching it to write this, I've really wound up admiring some of the directing tricks it uses (such as the brief first person race along the corridor with Hajime).

(Also, notice how many of the bystander characters in the background are moving themselves as Hajime dashes past them. In many shows, those characters would have been mostly or entirely static. And the characters are not just static pictures being repositioned on the cell background; they are animated and changing.)