"Wait, Saten-san knows something about this?" Shirai Kuroko asked, sitting up straight.
"Shirai-san, I actually tried to tell you about this earlier," Uiharu said, a mild hint of complaint in her voice. "But because your entire focus was on Onee-sama, you kept insisting we'd talk about work later no matter how many times I called your name..."
"Huh?! So Uiharu... you actually know the key mechanism behind these bizarre Esper incidents?!" Kuroko's eyes widened in surprise.
"Yes. I actually have the file saved on my phone," Uiharu said, glancing toward Takahashi Yuuya. "Takahashi-senpai gave the audio track to Ruiko and me a while ago, but he strictly warned us not to listen to it because of the risks."
"May I see that audio file?" Kuroko asked, leaning in.
"Here it is," Uiharu pulled out her phone and pulled up the digital track labeled Level Upper. Although she had been somewhat skeptical that a simple audio file could forcibly elevate an Esper's calculation tier, she had trusted Yuuya's warning and never played it. What if the dangers were real?
"So... this is it? The culprit behind a city-wide crime wave is just a song?" Misaka Mikoto blinked, looking at the screen with suspicion. She was well aware of the recent spike in violent Esper crimes, having personally intercepted a few minor incidents herself.
"It sounds completely absurd on the surface, but scientifically, it's not entirely impossible," Kuroko said, her brows furrowing into a deep scowl. "The comatose patients brought to the central hospital all exhibited severe, systemic brainwave distortions. While the exact neurological origin of an Esper's Personal Reality is still being researched, the calculations occur within the higher spatial dimensions of the brain. Since the brain is the physical medium for refining calculation output, using specific acoustic frequencies to manipulate neural resonance and artificially boost calculation capacity isn't entirely out of the question."
"Th-That's wild..." Saten mused out loud, her curiosity thoroughly piqued. "If that's really how it works, then it sounds like some mad scientist created the Level Upper and distributed it on the internet just to gather a massive pool of human test subjects for an unapproved experiment."
"..."
The moment Saten's casual deduction left her lips, both Kuroko and Uiharu froze, staring straight at her in stunned silence.
Saten, thoroughly embarrassed by their sudden, intense glares, scratched her cheek nervously. "W-What? Did I say something wrong?"
"No... according to Saten-san's hypothesis, the entire timeline of events fits together with terrifying precision," Kuroko said, her expression turning deadly serious. "An anonymous audio file capable of artificially boosting calculation tiers suddenly appears out of nowhere, spreads virally across the student body, and then produces severe, delayed neurological side effects. It really does look like a researcher using Academy City's Espers as unwitting lab rats to test an unverified system."
The doubts in Kuroko's mind suddenly clicked into place, connecting all the scattered clues from the past week into a single, coherent thread.
"If that is truly the case, this is no longer a simple matter of juvenile delinquency. We must investigate and verify the acoustic signature of this file immediately!" Kuroko stood up abruptly, grabbing Uiharu's wrist. "Onee-sama, I'm sorry, but duty calls! Uiharu, we're heading straight to the branch!"
"Ehh?! I haven't even taken two bites of my ice cream yet! Waaah!"
"There's no time to eat ice cream! The safety of the city is on the line!"
"Kuroko is as terrifyingly efficient as always," Mikoto sighed, watching her roommate drag Uiharu out of the shop. But she couldn't help wondering—was it really going to be that simple to solve?
"With Uiharu's high-level network manipulation and decryption skills, they'll locate the creator soon enough," Yuuya said to Mikoto, a calculating glint flashing in his eyes.
'Once they cross-reference the matching brainwave patterns among the comatose users, the core network will be exposed. Kiyama Harumi will be backed into a corner, and the AIM Burst will finally manifest,' Yuuya thought. 'An artificial entity formed from the compressed AIM diffusion fields of ten thousand Espers... basically a conceptual lower-tier Angel descending into the physical world.'
"I suppose..." Mikoto mumbled, glancing at Yuuya and Index before slumping onto the table in utter defeat.
"Well then, I should be taking my leave as well. See you tomorrow, Misaka-san~" Yuuya said with a playful, smug grin. He stood up, stretching lazily. Index, holding her rapidly melting ice cream cone, quickly trotted after him.
To Index, it didn't matter where they went, as long as there was delicious food and she was by Yuuya's side.
"That jerk is definitely mocking me... it's so infuriating!" Mikoto gritted her teeth, her bangs crackling with tiny sparks of blue electricity before she let out a long, helpless sigh.
'What on earth is wrong with me today?' she pouted, resting her chin on her arms. 'It feels like I've been led by the nose by him from the very moment we met.'
"Misaka-san, I'm heading out too. See you another time!" Saten said, watching Yuuya walk out the front glass doors. She quickly stood up and hurried out after him.
Outside the ice cream parlor, Saten's voice called out from behind. "Wait a moment, Senpai!"
Yuuya turned around, a bright, sunny smile on his face. "What's up, Ruiko?"
Saten stood a few paces away, her hands tucked behind her back. Her cheeks were flushed with a faint crimson blush as she stepped forward and presented a small, elegantly wrapped gift box to him.
"This... this is a gift for you, Senpai! You've been taking such good care of me lately, so I really hope you'll accept it!" Saten squeaked out. The second the box left her hands, her face turned bright red. She squeezed her eyes shut and ducked her head, terrified that he might reject it.
"Oh? Thanks."
Yuuya was mildly surprised. While it wasn't the first time he had received a present from a girl, Saten's sudden gift was certainly unexpected. He accepted the small box and unwrapped it, revealing a sleek, late-model handheld game console inside—the kind that was notoriously expensive and difficult to reserve. She must have done research on what high schoolers were currently eyeing.
"A portable console? I was actually thinking about picking up this exact model," Yuuya smiled warmly. While he wasn't particularly obsessed with video games himself, Saten's thoughtful sentiment was far more valuable than the device itself.
Saten opened one eye, and upon seeing his genuine smile, her anxiety evaporated, replaced by a radiant beam. "As long as you like it, Senpai! Well then... goodbye, Senpai!"
Feeling a wave of shyness wash over her, Saten turned and sprinted down the street.
'Is she getting embarrassed?' Yuuya rubbed his chin, amused.
Index tilted her head, blinking innocently. "A gift...? Is she giving Yuuya a present because Yuuya helped her out before?"
'Yuuya caused such a huge storm and fought those scary Magicians just to save me, but I don't have any money or presents to give him...' Index thought, her eyebrows furrowing into a worried knot. 'What can I possibly give to Yuuya?'
The innocent, carefree Sister was suddenly deeply troubled by her lack of funds.
'Ah... wait a minute,' Yuuya suddenly remembered something, his cheek twitching slightly. 'I was having so much fun teasing Mikoto and chatting with the girls that I completely forgot to harvest Uiharu's Treasure Chest...'
'I'm supposed to be hunting System Chests, not spending my afternoon acting like a visual novel protagonist,' he reminded himself. He opened his mental Virtual Map, scanning the surrounding district for active nodes.
'Huh? A new Silver Treasure Chest spawned nearby?'
"Come on, Index. Let me take you on a treasure hunt," Yuuya said, stretching his arms.
"Treasure hunt?" Index asked, puzzled. "Can you actually find hidden treasure inside Academy City?"
"Just follow along. You still don't know your way around District 7, right? This way you won't get lost next time you wander off," Yuuya said casually.
"I won't get lost! And I never forget a single street I've walked down!" Index declared, her cheeks puffing out indignantly.
A short walk later, Yuuya arrived at the exact spatial coordinates marked by the System node and paused, stroking his chin.
Standing directly in front of a bank of bright red drink vending machines was a tall, slender girl wearing a traditional, full-length miko outfit—a white haori paired with a vibrant red hakama. She was standing motionlessly, poking the coin refund button with a blank, emotionless expression after the machine apparently ate her change.
'Well, well...' Yuuya thought to himself, recognizing the girl instantly. 'It's Himegami Aisa... the wielder of Deep Blood.'
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Give me powerstones.
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