I saw you wanted error being geno stuff so here have this idea ive had inside my brain for years
I have a headcannon that reaper found out that error was geno because of his GLASSES (being the exact same pair that geno used), and at first being like "NO YOU KILLED HIM?" to later finding the subtle things that geno used to do being performed by error, stuff like hiding smiles with his scarf or jacket, etc, etc. Idk how that would work out but hey! if you wanna cook writing ab this idea i will read it :3
First off, thank you for the ask!!! Don’t me afraid to send more if you wish. It took me longer to wr8te than I thought it would cuz I wasn't expecting to make it this long eheheh.
Honest to God before this ask I didn't realize Geno and Error share the same pair of glasses I thought it was just a fan art choice. But honestly, now that I know this it makes things all the more cute yet sad.
The idea that Reaper remembers such a seemingly insignificant detail about Geno. The first time he saw Geno wearing the bright red glasses was when he dropped off some literature for the skeleton to entertain himself with. He can't let his beloved go mad with boredom, now, can he?
The first few times Geno tried reading without the glasses came at complete failure with the skeleton's vision steadily declining ever since his entrapment on the save screen. Eventually the glasses slowly became a persistent feature upon Geno's face, especially when Reaper bought entertainment.
He remembers his first thought at the time being how perfectly the glasses matched his scarf.
Geno's disappearance brought heavy sorrow to Reaper, the God knew in some way the skeleton wasn't dead. He would have felt it, he would have come to collect him, yet knowing that brought little comfort to Reaper. In the ever-expanding Multiverse, if he, a god of death, could not find him, who's to say he ever would?
In the time that followed Geno's disappearance, Error eventually made his entrance, still thoroughly in his mourning period Reaper found little interest in the skeleton excluding the fact that the little glitch brought more work on Reaper's already spilling plate.
Regardless of whether he wanted to or not, wherever Error went, Reaper soon followed.
Death and destruction ran rampant around every AU that Error visited, interfering with such chaos was not within Reaper's job description nor did he care to make such frivolous attempts.
With the consistency of Error's pace of destroying AUs, they saw each other frequently, they rarely spoke aside from minor banter, and from Reaper gently expressing his thoughts of the Destroyer, perhaps slowly his work down just a tad. Which was, of course, met with disgruntled mumbles and frustrated curses of his supposedly understandable motivations.
It wasn't until later on that Reaper grew interested.
Before starting his inevitable rampage, with Reaper following close by, Error stumbled upon a sort of fabric store, primarily for the usage of arts and crafts. Not that the Destroyer could see that, of course, the glitchy skeleton stared through the window for a solid few seconds, eye sockets scrunched in a squint. The Destroyer pulled out red spherical glasses, identical to the ones his missing beloved wore.
The god of death felt his soul drop at the sight. Logic would tell him that in the span of endless universes, surely someone would have the same pair, but in such a short span of time to find someone with the exact same pair was just as suspicious. A cluster of emotions filled the god, rage was certainly the most prominent. However, acting rashly so quickly was unwise, especially with the chaotic force that was Error.
"Where'd you get those glasses, destroyer?"
"WhERě'd I-? THat'S nONe of YœuR bUSinESs, yoU diRtY ğLiTCh..."
Reaper's casual smile twitched with irritation.
"I'm asking cuz I knew a guy with the exact same pair, was wondering if you'd seen him around."
There was an aura of dread around Reaper as he spoke, though error didn't seem to indicate that it bothered him much.
Surprisingly enough, Error didn't immediately respond by lashing out. The black skeleton rolled his eyes and begrudgingly asked for a description.
Error showed clear signs of disgust.
Reaper continued nonetheless.
"He isn't from an au, he's just a variant from the original timeline who got glitched out. "
Reaper continued rambling about the entire situation, it almost felt therapeutic to talk about Geno to someone.
Error humbly listened and begrudgingly gave his answer.
"Ć-cAn'T sAÝ I'vE eVEr meT a gLItcH liKe tHAt, beSIdEs wITh thE wAy The tIMeLinE of EVentS sOUNd, I cOulDn't hAve."
Error visibly cringed, either upon recollection or the fact that he was even telling a single soul of this fact.
"I wAS pRoBabLY stUCk iN the aNtiVoiD arOund thAt tiMe, wøULdn'T havE bEən ABle to mEEt hiM evEn if I tRiēd."
Reaper solemnly accepted the response, though there was a chance that Error was lying, it was highly unlikely. The Destroyer had no qualms of expressing his great conquests even at the risk of offending people, which meant he was likely telling the truth.
It hurt to know that Reaper had gotten nowhere in finding clues of where Geno went, even seeking revenge would have been sweet, but it seemed he was back to square one.
Over the next few months, the two grew closer and, embarrassingly enough, Reaper grew smitten with the Destroyer. It was perhaps wrong of him to see the similarities between him and Geno, but Reaper couldn't help himself.
From the way he hid his face in his scarf when flustered or smiling to his deadpan look when Reaper said something just a bit too audacious.
It was so beautifully close to being like Geno, yet still remained unique to Error, beyond the similarities. Reaper grew to like Error.
His look of concentration when crafting a new puppet, his vague attempts at providing comfort, his irritation when things didn't go his way. It was all lovable in a way.
In an ever-encompassing span of stars in Outertale, Error sat on the edge of a cliffside, while Reaper lay in the grass sipping on coffee.
"My mEmORy iS rEaLLy b-BAd."
"N-no I meAn r-R-really B-bAD."
Error pondered on how to explain.
"It's bad eNough thAt I dOn't reMEMber anYthiNg befoRE the AnTivoiD, I just reMemBer wAKing uP one dAy anD bęING suRRoundEd by N-nothing."
"D- doN't you piTy me. I'm Just stAting fAct."
Error snapped at Reaper before continuing.
"I don't actuAlly rEmeMber how loNg I waS in theRe for, timE Works difFerEntly in tHe anTIvoiD. To me it felt like an e-EterNity but I aCTually can't piNPoįnt hoW Long I was iN there for, siNce my memORy only staRts therE."
Reaper glanced at Error's blue scarf, the exact opposite color of red yet in terms of shape and texture the exact same to Geno's.
"Just asking out of curiosity but... Which of your eyes has worse vision?"
Error looked confused by the sudden question but huffed a response.
"My R-right oNe is worse by a mILe, my glaSses maKe it just BArely beARabLe. Arė you looKIng for my wEaKNess or sOMethINg?"
Error's eyes showed a distrusting squint.
"No, no, nothing like that. Just....curious.."
Reaper wasn't a thousand percent sure, but just the thought, the possibility, that perhaps Error of all people could hold part of his past beloved made his soul spark. Maybe he would never see the Geno he remembers, but just the thought of being there alongside new life that exists with what was once Geno satisfied him. Being alongside him, beyond the walls of the save screen.
At least now, just doing that is enough...
(I didn't exactly know how to end it so I've left it on a bit of a neutral ending)