Any HPMOR x TTGL crossover story that visits The Stations of Canon for either show requires a set-up that carefully balances the characters so that their relationships are in the proper relation.
Both stories are coming-of-age stories in a fantasy setting with a young protagonist who is exposed to unknown magics, who is swiftly thrust into new situations and who changes in response to those situations.
Since HPMOR follows the Stations of Canon of its parent story, JK Rowling’s Harry Potter, a TTGL take on HPMOR should follow the stations of canon of its parent story. The secondary question is: What is the parent story?
HPMOR was a meditation upon how rational actors would react within the Harry Potter setting, where only a few things changed. I think the more interesting story to tell would be to find ways to shoehorn the facially-irrational characters of Tengen Toppa Gurren Lagann — the show with the catchline “Go beyond the impossible and kick reason to the curb!” — within the setting and audience expectations of Harry Potter and the Methods of Rationality. What better way to subvert, invert, revert and evert the expectations of the reader?
The primary question is: Who is the cast?
You can read iterations on the cast below, or reach the most-recent iteration by following this link.
This was the original attempt at setting a cast.
The Defense Professor plays the inspirational Kamina; Harry is the inspired Simon.
Dumbledore is Lordgenome, the wizard who was greatest in the land, who fought the rules of magic in his rise to power, who lost and was subjugated, who now enforces those very laws. As the Grand Sorcerer, Supreme Mugwump, and Chief Warlock, he now rules Wizarding Britain from behind the scenes, keeping the Wizarding World from growing too large, from gaining the attraction of the Muggles.
Hermione is typecast as Nia, the only ~girl~. At the end of the timeskip, a phoenix comes to her and she is taken to become the voice of the True Laws of Magic. Harry and company pack up and take off to save her.
Note: This setup is unsatisfying because:
Draco comes from within magic; from a family that sees all this as normal. He comes from a position of privilege that he knows how to use.
Harry comes from outside magical society; while he is rich and famous he has no training in this particular power and what little he does have is book knowledge.
One is clearly the teacher, and one is clearly the follower. This sets up a Kamina/Simon dynamic, but who should lead?
In HPMOR, the Defense Professor is Harry’s teacher: an obvious Kamina character.
However, the Defense Professor also serves as Harry’s ultimate enemy. David Munroe/Voldemort/Quirrel sought immortality and was smacked down by higher powers, resulting in his present condition. This makes the Defence Professor an obvious Lordgenome candidate, which would nicely match the Stations of Canon by having Harry confront the Defense Professor at the end of the first year.
Another parallel between the Defense Professor and Lordgenome is how they got to where they are now. David Munroe sought power, raised an army, knocked on the gates of power, and almost won. He was stripped of his power, and sent to tend a garden, making sure that the garden grew within the boundaries of the Ministry’s educational requirements. Lordgenome fought the Anti-Spiral and lost, and was set over Earth to make sure that the population of humans did not grow too large.
If the Defense Professor is to be Lordgenome, Nia must be related to David Munroe, which leads to the next consideration.
While out gallivanting about, Simon runs across a character that Simon cannot leave behind: Nia. Nia serves as a mascot for the Spirals. Because Nia is the daughter of Lordgenome, Lordgenome’s servants don’t see her as a legitimate target. However, the physical details of their father-daughter relationship are left unknown; it’s assumed that she was adopted somehow.
If David Munroe is Lordgenome, or Harry James Potter-Evans-Verres, must be Quirrelmort’s adopted son. HJPEV already is that in HPMOR; why change their relationship any?
Who in the cast is new to magic? Who keeps going down rabbitholes following interesting ideas to see where they end up? Who is naïve and impressionable? Who has imposter syndrome? Who doubts their ability to do things?
No, not HJPEV, he’s already been cast.
Hermione Granger is the next-most-obvious candidate for Simon. She starts out lost, alone, withour friends but with good grades. She gets pulled into trouble, finds some friends, and saves the world. And for a rationalist story examining the problems inherent in applying rationality to a setting where if you don’t believe in and have faith in the magic, the magic stops working, what better character is there to be taught rationality than someone who wants to nail everything down and study it? What better person to raise up as a leader than someone who hasn’t even read How to Win Friends and Influence People?
Viral’s postion within Lordgenome’s forces is initially ill-defined, but in later parts of the story he’s pretty clearly been tasked with defeating Simon. The protagonists of Rowling’s Harry Potter had many enemies, but the one that shows up most often is Draco Malfoy and his goons. Their tasking comes from their parents, who served Voldemort in turn.
Post-timeskip, when Simon is broken out of prison, Simon sets Viral up as the pilot of Gurren, despite Viral being a Beastman without Spiral power. By the end of the story, maybe Viral develops that power.
Who’s close enough to Hermione to be a mentor?
Some people say Ron is irredeemable. That Ron is a doofus, a loudmouth, an inconsiderate jerk with no sense of what boundaries shouldn’t be crossed, a braggart who runs more on bravado than sense. Someone left with a relative’s half-broken wand. Someone who might make friends easily. Someone who bears the weight of enormous expectations, which may or not come form within. Maybe Ron is Kamina.
Neville doesn’t strike me as a Kamina, but he might make a convincing Simon.
Who else is fleshed-out-enough as characters in Rowling or Yudkowsky’s canon?
Thus, I propose a return to Harry James Potter-Evans-Verres as Kamina. Aleczandxr’s The Narrative Trick of Early Gurren Lagann gets well into the sort of character that Kamina is:
But if that happens, we lose Harry-as-Nia. Who would replace Harry as the adopted child of Voldemort, one linked inextricably through filial bonds but turned in opposition to him?
Hetero romantic option for Hermione-as-Simon? Check.
Tied to Voldemort as an ambiguous foil via a prophecy? Check.
Pure and innocent and burgeoning with Gryffindorian morals? Sure.
Although … on the subject of prophecy, TTGL did not have a prophecy mechanic, and HPMOR adapted the canon prophecy. If Neville as Nia is supposed to be a child of Voldemort as Lordgenome, then what better way for Neville to be introduced as the kidnapped child of the Longbottoms, stolen by Voldemort’s forces for some ill-defined goal, raised among Slytherins. “You’re all so … straightforward,” Neville says one day. “I want to live in a world where people can be honest with each other!”
In TTGL, Rossiu is found in a secluded underground city named Aida, which lacks external trade and is very resource-constrained. There’s a limit on how many people the ecosystem can contain; the village elder runs a lottery that can result in people being exiled. Presumably, they die. This happened to Rossiu’s mother. The village elder is the priest of the Big Face.
One day, Simon falls through the ceiling of the village, bringing with him the big mech Gurren Lagann.
The village elder is put in a painful position by the appearance of another Big Face; he climbs into the temple mech and tries to slay Gurren Lagann. He fails, and this shatters Rossiu’s worldview. Rossiu joins with Simon and becomes the replacement pilot of Gurren.
A character to fulfill the role of Rossiu must be:
Yoko Littner in TTGL is many things. She’s the mentor for Kamina and Simon when they first appear on the surface. She links them with an established surface faction and provides ranged support in their adventures. Eventually she pilots a mech, but her default mode of interaction even then is sniping.
This would seem to indicate a character who:
Harry and Hermione, both orphans in a Muggle world. Would need to do a lot of research on how modern-day orphanages work in Britain, but the gist of the idea is that they’re close friends. Harry is older than Hermione by a few months, so that they’re in different grades at school, but they’re basically inseparable otherwise. Harry sees Hermione as his ticket out of the home and his sister; Hermione sees him as an older-brother figure.
Hermione is hanging out after school one day, waiting for Harry to get out of detention, scuffing her shoes through the mulch, when she kicks a root that doesn’t budge. Kicks it again, it pops out of the ground: a curiously formed root; it’s so straight. Picks it up, casts something. Harry walks out of the school building, she runs to greet him just as the Hit Wizards show up to save the Muggles from an improper use of magic. There’s a short fight, in which Hermione discovers how to shield and how to cast some vague offensive magic. The Hit Wizards retreat for long enough that Hermione drops her shield, and Harry and Hermione walk home, discussing this thing.
Then, bam, Stunned. The Hit Wizards try to confiscate the wand, but it looks like it’s stuck to Hermione’s hand via accidental magic. Harry tries to fight off the Hit Wizards; it turns out he does have some magic in him but it’s purely accidental stuff. So he gets Stunned as well.
It’s near Hogwarts’ start of term. The Hit Wizards drop these two kids off at Hogwarts, where there are conversations that the audience may or may not hear. The Hit Wizards return with some of their stuff; eventually Professor McGonagall wakes up the children and lets them know what’s what.
That’s episode 1.
Harry was orphaned as in the main timeline. However, an individual with a mandatory reporting requirement triggered a child services investigation into the Dursleys in response to Harry’s bruises from Dudley’s bullying, and some time after Harry started going to pre-school or grade school, whatever Britain uses as earliest out-of-home educational opportunity, Harry was removed from the Dursleys and placed in state care, and then adopted by a “forever” family.
The Grangers realized that they could support another child, after having Hermione, but couldn’t agree on when to time the child’s birth for optimum impact on Hermione. Or they wanted another child, but had already self-sterilized. Or they had had a lot of trouble conceiving the first time, and decided to adopt. But they found Harry Potter on the list, and adopted him because he was the same age as their Hermione.
Harry James Potter-Granger found in the Grangers a loving family, willing to support his trauma and his knowledge-seeking.
Hermione seeks the theory. Harry seeks applicable knowledge. Harry’s a few months older than Hermione, which puts him in an older grade of class.
When the Ministry kidnaps Harry and Hermione off to Hogwarts, they Obliviate the Grangers as Hermione watches. This is the analogous trauma of when Simon’s parents were killed by an earthquake, which Simon realized (during the show’s timeline) was due to Beastman Ganmen stomping about overhead.
I think the realization of this trauma works with the best parallel if Hermione realizes over time that the reason that her parents are not writing back is not because they cannot, but because they don’t remember her. And because they don’t remember her, they don’t trigger the mail delivery owls’ guidance enchantments, because those rely on the connection between the sender and the recipient. If neither knows the other, the mail generally doesn’t go through. It’s an owl-flocking (spam) prevention measure that was an unintentional and emergent feature of how the guiding magic works, now intentionally unpatched.
In short, see this Reddit comment.
However, as written in that comment, there’s no reason for brooms, much like how with Muggle construction equipment available to all, there’s no need for people to drive cars.
Which means that there will be brooms in popular use for people who:
As an example from TTGL, Yoko Littner in TTGL rides a flying Vespa when she leaves to become a schoolteacher. She has no need, then, for the capabilities of a mech. She just needs a ride.