Do you think it's more likely that the first narrator is either Pareidolia or someone at the bottom of the well than that it's the Himawari that's within the cycles? Because there would be a Himawari outside of the cycles, and one that is at the waiting room (she shows up in the recent update, and it's where she's at in a flash during Ad Meliora). That would fit with the drain, and being unable to leave.
There is also the narrator from "Where the trees live", since "they" are the ones that send nao-chan, and they say they're speaking to him as people that are living in the same timeline as him, not from the future. It's either we have two Himawaris that narrate (one from the future and one from within the cycles), or the first narrator is narrating from the abyss? Which would make them either Pareidolia, Sekai or some version of Maya.
I think (but can't know for sure) there's only one Himawari and she exists outside of the cycles. Time between different worlds doesn't run in parallel (this was shown conclusively when Sensei went to Terminal 22 before his own birth) so she's able to access our world at different points in the cycles while time moves normally in her world (not at the same rate). Given where and when she shows up, I think her ability to do things in this world is pretty limited.
I imagine the first narrator was in the well or an abyss of some sort before the start of the game but since then has been experiencing the world through Sensei. Maybe they ended up there after death - Ghost Sekai has said her afterlife is just an unending pool of darkness. It's unlikely it's any version of Sekai, though, since the narrator says they never liked poetry.
I'm unsure on the narrator's identity. I think there are a lot of little clues that point to Maya, but it's unlikely to be that simple based on the way the narrator speaks some of the time. Maya Prime would never in a million years (heh) talk like this:
The one thing I'm reasonably confident on (for reasons that are too complicated to try to write up right now) is that the narrator is connected to USER4, which probably makes them part of the "we" who sent Nao-chan. I personally don't think Himawari is part of this group, but I could be wrong. Leading candidates: Ami, Maya, a combined Ami and Maya, or someone we haven't met at all outside of narration.
In regards to the "Where the Trees Live" narrator: they say something like "I say this not as someone who knows the future but as someone experiencing the present with you". That doesn't mean that they exist in the cycles outside of watching through Sensei's eyes. It also doesn't necessarily mean that they don't know the/a future, just that it isn't influencing what they're currently saying.
Then we have the realities where Sekai is dead. Well, the difference between all of them is that when Sekai is alive, Maya doesn't exist. And when Sekai is dead, Maya is there. If we couple that with the fact that Ami seemed to have "Maya's place" in the cycles where Maya wasn't there, and the fact that Ami seemed to have been experiencing the cycles for much longer than Maya (the scary room scene in the last update), we can conclude that the cycles started from a reality where Maya didn't exist and Sekai was alive. Then, at some point, Maya started existing and the past got altered. I don't know if the past actually got altered, or it's just their memories of the past that did though.
Technically we don't know for sure that Maya doesn't exist in the alternate timeline. It could be as simple as Sensei never had a relationship with her because Sekai was still around, which also means she never would have met Ami.
If Maya doesn't exist (probably the case), I think there's a simpler explanation for it: Sekai's death was the catalyst that led to Maya's creation, not the other way around. Because Sekai never died in this timeline, the events that led to Maya's existence never happened.
For one, if Sekai's dead there's a clear motive for Maya's creation, namely filling the hole in a broken Akira's life. I think it goes even further than that: before Maya's existence Akira filled the hole by having a sexual relationship with Ami. Eventually he was overcome by guilt and somehow changed the past to create Maya as the perfect wizard girlfriend so that at least the girl he abused wouldn't be the daughter he was supposed to protect.
I think that explains narrator Ami's reaction in "Wake Up (My Story)"; she's not saying that LiL as a whole is supposed to be her story, but rather this memory in particular. She's angry that Maya has replaced her in a scene which is
supposed to show a relationship between wizard Ami and Akira. A scene that likely wouldn't have ever happened if Sekai was alive. It also explains why Ami doesn't appear in any of Akira's recovered memories; her original role has been "stolen" by Maya.
If you're correct that the alternate timeline shows the original main timeline before the past was altered, the change can't be as simple as Maya going back in time to cause Sekai's death. The divergence occurred long before that when Akira agreed/refused to go to Kyoto (or maybe even earlier). From what we saw, the most important thing that led to his decision not to go was his relationship with Niki. I don't see how a time traveling Maya could have affected it.
Instead I think this literally is an alternate timeline - a "what if" of Akira choosing to go to Kyoto. That's supported by the narrator talking about infinite worlds that exist as a "library of outcomes" where things happened slightly differently.
She keeps rebooting because she's also a shadow, according to Ami, at least. It was implied that the main characters of the cycles were Akira and Ami. Sekai, as everyone else, only had a part to play. If you remember correctly, Sekai mentioned the police and Ami ruining everything for them - her concerns are regarding real world consequences, whereas Ami is aware that everything is playing in repeat.
I interpret these lines to mean that alternate timeline Sekai knows that the world has to be reset as a result of Ami's actions.
Ami was looking forward to Christmas but now it's not going to happen "this year" because time is about to be rolled back to earlier in 2020 by "SANTA", which I assume means god(s).