This one's a little bit different. It's not explicitly set in TTS, but could just as easily be worked in as a side story. Basically, with all these virtual waifus we've got to satisfy ronrey Otaku, you have to wonder: what would the Adeptus Mechanicus do if they found such technology?
Scene: The planet Grorious Nippon
Magos Caligulus of the fourteenth Explorator fleet had discovered a treasure trove of acheotech. Progress was slow, however, as the inhabitants spoke an obscure dialect of High Gothic. While they had seen the script before, it was mixed haphazardly with standard Gothic and contained many words with no direct translations.
The planet attracted the Mechanicus' attention, as early reports stated that various new Titan patterns were discovered here. However, what they found were mostly incomplete parts intended for aesthetic design over functionality. The only working models were hasty conversions of existing Titan patterns.
Nevertheless, Caligulus was determined to find something of value on this planet. He entered one of many abandoned building; it appeared to be some sort of temple to pagan deities, with many illustrations on the walls depicting colorful pubescent girls. One thing though caught his attention: In the center of the room was a pedestal, a terminal of some sort. In the darkness, his auspex could make out that the pedestal was surrounded by human remains. Some of them appeared to be fighting each other.
This did not bode well, but Caligulus pressed on. The Quest for Knowledge demanded it. He needed to identify what the terminal was for, owing to its obvious importance. Caligulus extended a mechadendrite and attached it to the nearest I/O port. He restored the facility's basic functions, and in moments, the terminal began buzzing and whirring to life. On top of the terminal was a holovid projector. When activated, it projected a figure that was lying down.
Caligulus was intrigued. The figure yawned as it sat up, though its back was turned towards him.
Suddenly a high-pitched voice came from the terminal's speakers. <"Eh? Moshi-moshi? It's so dark in here. Where did everybody go?">
The figure turned around and faced Caligulus. Though he was a senior tech-priest and thus had emotional inhibitors installed, he was shocked by what he saw. The figure was a noseless, large-eyed creature who spoke in a shrill voice! Was this some sort of Tau?
But he wasn't the only one to be surprised. The figure leapt back and cried, <"AH! A TENTACLE MONSTER! YAMETE!">
Caligulus' cogitators processed this information. No, this couldn't be a Tau, that was impossible. This facility far predated the Tau. Besides, this figure had human flesh tones, and a full head of hair. This must be s machine spirit, albeit an eccentric one.
"Do not be afraid, Ancient One," Caligulus replied in his most reverent frequencies. "I am Magos Caligulus of the fourteenth Explorator fleet. By the will of the Ommnissiah, you have been awakened after twenty thousand years of dormancy."
<"Twenty thousand years?"> she said sullenly. <"Then... Onee-chan... he is..."> the machine spirit began crying.
Caligulus was now troubled. Never before had he heard of a machine spirit acting this way. He knew of machine spirits that could lash out if mistreated, or avenge their fallen user, but a machine spirit mourning the loss of a mortal was unheard of.
"If I may ask, oh Revered One," Caligulus asked, "What is your identification?"
<Moe-Tron,"> the machine spirit sniffed.
"Was this Onee-chan important to you?" Caligulus asked.
<"He... he made my kokoro go doki-doki. He was my special someone.">
Caligulus felt uncertain for the first time in over a century. Was he experiencing... heartbreak? Over a machine, no less?
<"Please, will you stay with me?"> Moe-Tron begged. <"I don't want to be alone, uguu~">
At that moment, Caligulus made up his mind. He ordered his crew to remove the terminal and bring it back to the ship for further study. The report he gave to Mars told little of what he experienced.
"The machine spirit we found seems to have been intended specifically for human interaction. However, due to the language barrier, progress has been a little slow."
"We can send you a lexmagos to assist you in your research."
"... that will not be necessary. I am focused on acclimating the machine spirit to the present, so the fewer new visitors, the better."
"Undertsood. But we expect regular progress reports."
Caligulus locked himself away with the machine spirit for the next three weeks. Though such behavior was not uncommon, his reports started causing concern. His speech became more erratic, as he would slip into the obscure dialect and use words like "otaku", "mecha," and "3DPD" without regard to congruity or context. He also stated to ramble on his reports about "changing everything we ever knew." The priesthood of Mars became concerned enough that they sent a delegation to investigate Caligulus. Though his subordinates unsuccessfully tried to bar them, it became a moot point.
"I HAVE HAD A REVELATION!" Cried Caligulus as he burst forth from his sanctuary. The delegation was immediately shocked by his change in appearance. His frame became more heavyset, while his robes were stained and I'll-fitting. Small unkempt mechadendrites extended from his neck. His exterior secreted motor oil, which left a foul smell.
"Brothers, by the will of the Omnissiah, I have discovered the path to greater unity with the machine! Here on Grorious Nippon, we have found machine-spirits made for the explicit purpose of companionship with mortals!"
The delegation looked at each other, uncertain of what to make of this. They would record the entire incident and have the elders render judgement.
"The path of the Waifu shall bring man and machine together as one! And so, it shall be my purpose to spread this revelation! Behold: Moe-Tron!"
Behind Caligulus emerged the strangest sight yet: a six-foot tall robot wearing a frilly pink dress, with its head replaced with a holovid projector displaying Moe-Tron's face.
<"Ohayo! I am Moe-Tron, desu! I am here to share live and joy with the whole world!">
Caligulus performed a live most unbecoming of a tech-priest, and leapt upon the robot in a passionate embrace. "Isn't she the most kawaii thing ever?! I love you, Moe-Tron!"
<"And I love you too, Onee-chan!">
The delegation was too confused to do anything. Instead, they hastily left to report what they saw back to Mars. As the elders deliberated on this strange development, Caligulus was already spreading the Path of the Waifu to other tech-priests. It spread like wildfire, especially among the younger male tech-priests.
It wasn't until Caligulus declared to have found a repository of waifu machine-spirits that he planned to share with everyone, that the priesthood acted. Fearing another Moraie Schism, in desperation they called upon the inquisition to assist.
Inquisitor Antiachos was already listening in on the developments; if the forge world's became more focused on their waifus than on production, it could lead to disaster for the rest of the Imperium. Worse still, these activities sounded too similar to the Men of Iron of old, and rumors of unsavory acts done to the waifus sounded outright heretical...
One of his agents intercepted information on the repository that Caligulus found. "Look here," he said. What is this indicator?"
"'Personality subset,'" answered the scribe. "The terms used here do not have any direct translation. There's 'Tsundere,' 'Himedare,' 'Kuudere...'"
"What about this one here? It appears most frequently."
"'Yandere'... best translation is 'one who loves to the point of violence.'"
"That can't be good. And they want to put those things into physical bodies? We need to warn Mars immediately."
But it was already too late. Caligulus' followers had already started fighting amongst each other, about how their waifu was superior and all others were shit. Some began hoarding waifus, while others fought over the same waifu. Petty shouting matches turned into violent power struggles. Waifus started being uploaded into tanks and Titans, and all hell broke loose.
The subsector is now mostly abandoned. Of all the waifu cultists, only Caligulus himself remains.
"How could this have happened?" Caligulus cried. "I wanted to spread peace and love! It wasn't supposed to turn out this way!"
<"Don't be sad, Onee-chan,"> Moe-Tron said, <"we still have each other!">
"I guess you're right," Caligulus answered, still depressed.
<"I know what will cheer you up, let's sing the Lucky Star theme together!">
"You always know how to brighten my day, Moe-Tron."
And thus ends the tale of the Great Waifu Schism.