i'll go with a pure "slice-of-life" au rewrite, just because it's easier to answer. so i'll reframe it like this:

how would kanata and keito meet, if they lived "normal lives". i'll still put kanata in his cult, but it's more of a madara/souma adjacent vibe, not "he is the living god and has been raised to be beyond human skills". it's just his religion, and he doesn't play a key role. they'd be mid/late-20s, because we love 30s ennui yaoi.

keito probably would've gone to university? okay. I have this non-idol au I made with a friend. he gets a good, high-paying job. it's not notable to him or his skills at all, it's just a wealthy business that's doing well. nondescript. he has no general satisfaction with his life besides his manga he does on the side and his partner: a beautiful gf, almost-fiance. nice dates, kissing on moonlit nights, fancy watches and coats. totally fumbles her, keito style. he quits his fancy job bc he lost her and decides he doesn't want to live an entirely miserable lifestyle.

so he just opens up a small independent manga circle. he moves out of a good apartment, and lives in a more shoddy one so he can make his nest egg last. he's gone from nicely prepped suits and watches to bedraggled office worker vibes. he's picked up smoking. he still wears slacks and a button up, but the sleeves are rolled up and his belt is the only thing that pulls the outfit together. floppy bangs in his face, a little sweaty from the muskiness of the apartment. he gets everything sorted out, rolling out a desk into the small living room. he sighs, hands on his hips. his socks are mismatched as he sits crisscrossed and works.

he hires like, one editor and a screentoner, one of which is... ISARA MAO, WOOOOOOOOOOO. mao is his primary editor and proofreader. he went to art school for photography, and he was just looking for a job. pay is eh, but it's right up his alley and the boss is nice. he'd like a raise though. cue another entrance SENGOKU SHINOBU WOOOOOOOOOOOO. shinobu is also involved, he worked at the same business as keito. shinobu sees keito leave the agency and leaves, one of those spontaneous "if I don't leave now, I never will, I'll be a coward all my life!!" scenes, y'know. huge life choice at the drop of a hat. AND THEN HE'S LIKE 'WHY DID I DO THIS IT DOES NOT PAY WELL' WHEN HE'S ACTUALLY THERE.

they have lots of slice of life comedy shenanigans. keito sees his ex, is in a funk the whole day.
shinobu: [was gonna ask for a raise]
shinobu: ......... maybe another time

ANYWAYS

for kanata, I always love him working at his aquarium. it just feels good, he has something that's his own. in this AU he begs his family not to sell it: he's going to make a good turnaround on it. they agree (he's never asked for anything up to that point), but he has to do it on his own. madara and souma, childhood friends, would probably work with him. kanata does most of the work as its curator: accounting, inventory, making itineraries. he's sort of forced to pull it all together even if he's bad at functioning with structure. this matters to him!! the fish need him!!

kanata doesn't have as many issues with monotony. he says hello to madara, he says hello to souma when they come into work. he says hello to the fish as the aquarium opens. he says hello to the kids and parents and couples and school trips that come by. thriving business is good business. they're schools of fish going about daily routine. what ISN'T routine is the guy sequestered in some of the aquarium hidey-holes where you can look up at the fish. a handful of schoolkids just crowd around it like ??? when is this guy gonna leave.

keito's there to take reference pictures for his doujin. ordinarily, it's mao's job, but keito was impatient and needed to get out of his flat. he's already a little depressed because it's a date scene, so at such a popular dating spot, he's just... funk mode. he does not want to be there. he' sitting in his hidey hole, watching sea turtles swim above him. the kids just stare.... and leave to find another viewing spot. kanata watches as they scatter, and then bends down to peek... and join him in there.

they don't make conversation-- keito does NOT talk to strangers. kanata notices he smells of smoke and depression. lol. he just keeps his thoughts to himself, pulls his knees up.

"... it is not "nice" to hog these spots."

"i was here first." an incredibly petulant thing for a man nearing 30 to say.

kanata sprays him with hand sanitizer.

"there are other people here, don't come smelling like this again" he looks up at the creatures with him, and points them out for him. end scene.