In the spirit of not doing my blogging only on Twitter, I'm copying what I said about SSSS.Gridman's ending and it as a whole to here. The actual tweets start here, and there are interesting discussions with people who replied to me that I'm not copying here.

There are some spoilers here, but that's how it goes. Some expansion on bits of the tweets that involves spoilers is hidden behind HTML abbreviations.

SSSS.Gridman episode 12: Oh wow. Certain portions of that were kind of as expected, parts were pleasant surprises of the Gridman 'no beating around the bush' variety, and then the extended ending was really something else (something great). The final coda, too. Good work, Anti.

In the end SSSS.Gridman made the extremely smart choice of basically not explaining a lot of things, which I am perfectly fine with. It nailed the emotional and practical landing, and in retrospect it was carefully never framed as having mysteries.

To expand on this, SSSS.Gridman had things that it didn't explain, but it never presented those things to us as mysteries. No one ever asked 'why X' or 'how did Y come to be' or 'where did Z come from', and since those questions were never asked and were never part of the plot, it was easy to not answer them without letting people down (or at least I didn't feel let down). If a show is going to have things it doesn't answer, carefully keeping them in the background is in my opinion the best approach. Call this the anti Checkov's gun principle; if you don't want to have to shoot the gun, don't put it on the mantelpiece.

I still think the SSSS.Gridman OP and ED are probably saying some interesting things, but I'm not sure about it and the final episode didn't provide clarity. But they probably are strongly talking about the show's overall theme.

Before the last episode, I increasingly came to think that SSSS.Gridman's OP and ED were pretty meaningful; they not just had things to say about the show itself, but also gave us hints about what was really going on and had happened before the show started. In light of everything in the last episode, I no longer think that this is literally true. For more on the ED specifically, see Emily's great article on it.

Also, I know just enough about the surrounding context of the overall Gridman series of shows to know that the very ending of the show is perfectly fitting and a great callback. (I actually wondered earlier if the show would go that way and yep.)

As covered in Sakugablog's notes on episodes 5-7, among other places, SSSS.Gridman contains a fair number of fairly important links to the original live action Gridman the Hyper Agent.

Oh. I suddenly realized the obvious reason and meaning for why Anti stayed behind in the end of SSSS.Gridman, given what Anti is. Well done, show. And I bet he's going to hang out with Rikka to a certain extent, which ... really makes sense and casts another light on him & Rikka.

The expansion of this, which involves a more detailed spoiler:

It's strongly implied that Anti is effectively a piece of Akane's heart. Akane had to leave her dream world, but at the same time she loved it and sort of wanted to stay in it with the people there. So, with Anti staying, a piece of her heart is staying in the dream.

Back to my thread:

In fact, looking back a whole lot of Anti's interactions with Rikka are now really quite interesting if you look at them from the right angle. Poor Akane, in a way.

Another SSSS.Gridman thought: Alexis Kerib could be a metaphor or it could be real, and in fact it could be a mixture of both at once. Certainly as a metaphor, Alexis is eternal, as it said. And you cannot just beat it up; the real fix is something else entirely.

As a metaphor, Alexis Kerib is clearly the whole cocktail of depression, self-hatred, isolation, and so on, a cocktail that is eternal and cannot be directly defeated, only banished from the current sufferer. SSSS.Gridman did amazing work in showing us how much Akane hated herself and suffered from this cocktail all on her own.

In light of the very end of SSSS.Gridman, I think we have to rule out certain interpretations of the OP and ED. They now seem at least unlikely to be portraying Akane's real pre-series life, although they can be metaphors touching on it.

Also, the show gave us the meaning of SSSS, and it was well done. SSSS indeed.

Also, another important thing to note about the ending, from a Twitter conversation thread:

I choose to believe that the ending shot implies that there is, since Rikka's present is there in Akane's room as she wakes up. (Perhaps that present is in fact the trigger, lingering in Akane's subconscious all this time.)

You can read this many ways, but if nothing else the show wants us to know that the transit pass case Rikka bought as a present for Akane and finally gave her lingered into Akane's new life. It is very explicit about showing it as the first thing visible in the final scene of the show.

(And, in light of SSSS.Gridman's unusual soundscape, it strikes me as potential interesting that this final scene does have a background music track. Of course this might just be for practical reasons, in that there's no particularly appropriate basic environmental noises to use and dead silence would feel wrong.)

Update: Sakugablog's episode 12 coverage has a nice rundown on what we can reasonably piece together about the narrative from clues and allusions in the show, and also the things we have no idea about (of which there are any number).