Yesterday I found out about this story and read it all the way to the end. I have not read it a second time based on a clear understanding of the mechanisms, and I'm kind of awestruck by the difficulty of writing (in a clean but intelligible way) the kind of story that I seem to be reading.

If I'm understanding correctly, there is one Nargle in... in Hogwarts... and maybe in all of time? 

This is a monster (1) that has an attack that messily removes the attacked thing from time itself and also (2) has an ability to home in on the location of anyone who knows it exists.

So, on this theory, the key to realizing that in the future you will be fighting a Nargle is to notice "confusing absences" in your day to day life. Yet also: you cannot prepare for this fight very much in a cogent way because the more you realize that you will be fighting a Nargle, the easier it is for the beast to track you and precipitate the conflict.

The messiness of a Nargle Attack is key in several ways: it makes it possible for a reader and a character to notice the thing at all. Also the toleration for mess probably makes the story much easier to write. So this is a time travel story, and we only see the messy stable final post-Nargle-defeat "time loop". 

It is plausible to me that lsusr's total writing strategy was: write the story up until the Nargle deletes something from ever having existed. Save that as Story N. Edit the story in a backwards pass, as Story N+0.5, simply deleting stuff, and leaving notes to the author about the need to patch things. Then edit forward again to Story N+1.0, patching up the consistency as per the backward pass's TODO notes as best you can.

In general, as an author you're allowed to leave memory damage, confusion, and "mess" of some sort, and then you're also allowed to have some people notice this mess, and act somewhat differently. When the Nargle is finally defeated and nothing will ever be deleted from history again we call that Story F (for Final).

Maybe you edit Story N+1 all the way forward up to the Nargle Attack or maybe you branch prior to the attack if historical coherence simply becomes impossible to manage? Not sure. I'm going to posit that branches can happen as "a way for someone to survive a (counterfactual?) Nargle Attack" and the result is that they seem... "loony"?

Here's a possible survival strategy: find an object whose absence would dramatically change your life arc, that was in your life before you found out about the Nargle, and throw it at the monster during the fight so the monster unmakes it.  This unmakes that version of the fight, giving you another run at the beast.

Also, if someone is going to successfully fight, they will have prevented themselves from coherently knowing that they are in the fight with the Nargle (and thus being swiftly hunted down), which could add to the external appearance of looniness, as additional observational epicycles "from the perspective of outside observers"?

Under this general theory, we may NEVER have seen "the original fully non-loony Luna". Not in Rowling's fiction, nor in Eliezer's fic, nor in this story.

Under this theory, this was Story N=F, and all other fics are Stories where 1<N<F because those are all stories where Luna is visibly loony (hence has been attacked by the Nargle in a previous time loop already) AND things like the entire House Of Hufflepuff still exist (which, if I'm reading correctly, was deleted from history in the final battle).

It seems to be suggested that somehow Atlantis's deletion from history was a result of The Nargle attacking it EITHER (1) long long ago, or (2) maybe somehow Atlantis was deleted during Luna's battle?

I went back to read Part 6 of this story, and I'm not sure if Harry thinks that Atlantis was deleted from history (as in HPMOR canon) or not.  It could be that the Harry in Part 6 has "the signature of a messy deletion" where he believed that Atlantis existed in some early loops... then the event where "Harry shows the Mirror of Atlantis/Erised to Ravenclaw's Heir" persisted as a recurring event despite all or most possible Nargle Attacks all the way up to Story F, which we have read?

Plausibly: Kirito wasn't just "Luna's friend" but was actually the Heir of Helga Hufflepuff. Tom Riddle is pretty clearly Salazar's Heir. Gilderoy Lockhart is plausibly the Heir of Gryffindor? Luna found the Diadem. Thus: all four heirs (all five heirs? (all [as many heirs as exist in Story 0] heirs??)) were needed to defeat the Nargle. Thus: Kirito was the Heir of Hufflepuff.

Tom and Gilderoy and Luna all have a swiss cheese of memory backups and public lies and apparent private confusions and so on, where a normal person would have a coherent personal narrative and common sense beliefs. Having just read the Story Where N=F (which is the smallest and most messy of all stories because it has the most Nargle Damage?) Kirito's "narrative gaps" are the biggest: he doesn't even exist anymore... and neither does Helga Hufflepuff?

In Part 2 there are many ellipses in what the Sorting Hat says and then, "Do you say that to every girl? Luna thought, Do you call all of us complicated and courageous and talented and—" so she is interrupted before she can say "loyal". This is, I think, part of the deletion of the house?  But then the unnamed Hufflepuff Prefects (not that Luna remembers people's names much anyway) go behind the Barrel in the Kitchen Hall... and then after the vinegar prank that's the last mention of House Hufflepuff?  (I think? I'd need to re-read to be sure.)

This seems to make House Hufflepuff the most heroic of ALL the houses in some deep sense? Like... the apparent gentle contempt that everyone holds for "the house of loyalty and hard work" during various Stories Where 1<N<F... this can now potentially be read as a sort of an echo of the mild contempt that almost everyone also has for Luna?

This whole reading of the story is full of wild suppositions. It is plausible that re-reading a second time, looking for falsifications, would cause the theory to need to be amended.

Professor Quirrel took the diadem in his hands. He feinted as if to place it over his head. Then he tossed it back to Luna.

“I am an Occlumens,” said Professor Quirrel, “Ravenclaw’s device rips the incoherence out of doublethink. If I were to place this device over my head I would be lucky if it did not shred my mind. Nice try.”

That is the Professor Quirrel we know and love.

Thanks for writing and finishing this story! There's something particularly commendable about the act of finishing any kind of project. Kudos!

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"In the First Wizarding War, your mother contributed to the development of a secret weapon intended to neutralize Lord Voldemort." (chapter 4)

Given the incompetence of the wizarding world, it seems very appropriate that the way they'd come up with to defeat a powerful evil wizard would be to... offer him godhood and make him someone else's problem.

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Alternative story ending: Lord Voldemort defeats himself by using Legilimency on Luna.

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The curse on the position of Hogwarts' Defense Professor still seems to be active. How unfortunate for Mr. Lockhart. Though what was he thinking when he accepted the position in the first place?

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Does anyone know what the 7 and 0s thing on the astrolabe is a reference for?
Same question regarding the tactical reality anchors.

I'm so confused. How did Luna survive the Killing Curse?

I don't understand. I was quite intrigued about platform 9 and a half, about detecting things by explicitly ignoring everything of interest, really nice ideas. I'm usually able to read fics in English and understand most of it, but in this case, I fear I failed a lot. I do not know whether it is because some things were removed from history or whether it's because it 's a LL point of view. I can imagine that it's a really good point of view, but that's too confusing for me to follow. It's not even clear to me what occured at the end

Luna stepped out of the Forgotten Library. She held the Sword of Gryffindor in her left hand and Wanda in her right. She buried Wanda in Hagrid’s pumpkin patch.

Ow. I feel stupid now. I didn't expect that. Great foreshadowing.

That was fun. I enjoyed that. Thank you.

There's something very satisfying about an end for Quirrell that he can control. I always thought he deserved better than that - better than passivity. You've improved it, in my eyes!

Nice story. I want way more Luna, plus puzzling interactions with Tom Riddle and unicorn.

What finally happened to the nargle?

Typo:
"Then he tossed it back to Luna. [...] Professor Quirrel tossed the diadem back to Luna. Luna kowtowed." -> He tosses the diadem back twice.

How does Hagrid tame the nargle?