Prelude to the First Night
Throughout Titus' impassioned spiel about how the recording crystal was a priceless glimpse into the secret history of the guild members and blah blah blah, Albedo could not give a single shit about it. Once again, everyone was so obsessed about how great those traitors who hurt her beloved master were. She smiled like an angel, imagining Titus' shocked reaction if she smashed the crystal right in front of him. But Titus was useful to her, so she decided to "lose" the crystal instead. Destroying Nazarick's history was essential in her unceasing efforts to make Momonga the only Supreme Being.
But Albedo did not know Ainz had told the librarian to become friends with Mare. Mare was a child who existed to disrupt everything around him. He would wake up at three AM to read books for an hour, then he'd spend the next two hours plotting how to screw up everyone's plans. At five AM, his sister would wake up to start her work day. She would try to get him out of bed, but he would completely ignore her until she gave up. Then he'd actually sleep until ten AM, where his sister would nag him for two hours until he finally stopped pretending to be asleep and get out of bed. He enjoyed the daily ritual of annoying his sister while playing innocent, and he even trolled Demiurge on an occasional basis. He actually worked harder than anyone else in Nazarick, and still convinced everyone that he was lazy. Sadistically toying with others was his sport, and no-one in Nazarick was the wiser – except Ainz of course. The other member of this diabolical pair, Titus, did nothing but memorize every single sentence in that library. He claimed that that he was the third smartest undead in Nazarick and that Shalltear and Ainz were above him in intelligence; Shalltear because afraid of her, and he was genuinely wrong about Ainz. At four AM every day, Mare would visit him and they'd plot together. Between the two of them, they knew practically everything about Nazarick. Because he was such a huge nerd, even though Titus had only seen the crystal once, he had already memorized the item's entire description.
Within one hour of Albedo losing the crystal, Titus had told Mare these fateful words:
"It was a fantastic discovery! The Supreme Beings left behind a recording crystal containing thousands upon thousands of images. I can't wait to hear about Hentai Kamen, Boku No Piko, Twilight..."
Titus knew not the horrors that he would unleash with those three words. For centuries, evil neuroscientists had been messing with brains to create the perfect supersoldiers, so they had practically mapped the whole thing already. The nanomachines that Yggdrasil players used were capable of taking over the human brain and everyone wore helmets to prove that they weren't responsible for going on killing sprees. Society was so awful to live in, people would play video games with potentially lethal consequences to have a brief respite from their lives.
When Bukubukuchagama had seen everyone's reactions to Boku No Piko, she imagined a world where everyone would be forced to watch it endlessly. Mare was equipped with Tentacle-related magic to trap everyone there until they had watched the whole thing, and memory magic to make them think they were watching it for the first time, again and again and again and again until they finally ran out of nanomachines. When it was finally over, the helmets would restore any lost memories, and Mare's victims would remember watching Boku no Piko for hours on end.
Now that the denizens of Nazarick had been given immortality in this new world, those hours of torture could turn into years of horrifying repressed memories. This was why the guild had created the Neuron Therapist – Neuronist. Only she could end the horror.
Those three words primed Mare's primal instincts. On the next meeting of the guardians, Mare said "Let's have a movie night!"
And so it was decided. The guardians prepared their snacks and sat down on the couch. Little did they know, they'd soon be trapped in an endless loop.