Also throughout the story it's "Batman" and not Bruce or Peter, and I think it's because he's in Peter's body. He doesn't "accept" he is Peter, and because he isn't Bruce Wayne/body so it's just Batman this, Batman that...
*****
Chapter 1: Crossing Over
Gotham was always raining.
Batman merged with the night, standing motionless atop a gargoyle sculpture as he surveyed the rain-swept city below.
This surveillance was part of his routine, something he did three hundred and sixty nights out of every three hundred and sixty-five days a year. But tonight, something went wrong.
Without warning, the world around him became a kaleidoscope spinning at impossible speed. Scene after scene flashed before Batman's eyes like a carousel of memories.
Catwoman, Harley, Zatanna, Wonder Woman, Talia... moments spent with them at different times, different places, spanning hours or entire nights.
Corrupt judges taking bribes, psychiatrists bought and paid for, cops looking the other way, officials in bed with organized crime.
Joker, Two-Face, Penguin, Scarecrow... criminals locked in an endless cycle of crime, arrest, and escape.
The rapidly shifting images made his head spin, but Batman remained perfectly still, quietly raising his guard.
The scene shifted again. In a cramped, aging apartment, an unfamiliar elderly man spoke to Batman in stern tones:
"If you have the ability to help others, then you have a moral responsibility to help others. This isn't a choice. It's a responsibility. With great power comes great responsibility."
But in the blink of an eye, a gunshot rang out. The serious old man collapsed in a pool of blood, weakly grasping Batman's hand:
"Peter..."
"Peter!"
A shout pulled Batman back to reality. Though the name wasn't his, he instinctively looked toward the source of the voice.
A middle-aged man in a white lab coat, slightly overweight, was staring at Batman with concern and worry in his eyes:
"Peter Parker, are you alright?"
Peter Parker?
Batman quickly sized up the middle-aged man. His keen vision caught the name on the lab coat's badge:
Otto Gunther Octavius.
Who was he?
Question after question rose in Batman's mind. Looking down at himself, he found he wasn't wearing his Kevlar and titanium armor. Instead, he wore an ordinary plaid shirt.
This wasn't rain-soaked outdoors either, but a brightly lit laboratory.
'Scarecrow's fear toxin? Or Mad Hatter's mind control?'
Batman didn't panic at finding himself in unfamiliar surroundings. He rapidly assessed everything around him:
A clean, bright laboratory. The walls displayed portraits of famous scientists, including the man before him, Otto Gunther Octavius.
Batman recognized some of the scientists, like Einstein and Newton, but others he'd never heard of: Bruce Banner, Hank Pym, and more.
Various experimental equipment lined both sides of the laboratory. At the front stood a large device resembling an inverted octopus, with a whiteboard beside it covered in calculations.
'Otto, the world-renowned nuclear physics expert? That device is a Tokamak reactor?'
Batman ignored Dr. Octavius, rapidly processing his analysis. His gaze landed on the formulas covering the whiteboard.
Wayne Enterprises had once attempted to develop fusion energy to benefit Gotham.
Unlike Dr. Octavius's small Tokamak device, Wayne Enterprises had used magnetic confinement fusion technology. The scientific formulas for the two approaches were completely different.
After shutting down the fusion project, Batman had studied it independently for some time. He understood Tokamak-based fusion quite well, and spotted only one inconspicuous parameter error on the whiteboard. Everything else was flawless.
Though the parameter error skewed the final calculation, the existence of the formula itself allowed Batman to rule out the possibility of being trapped in an illusion.
Neither Scarecrow nor Mad Hatter possessed the ability to create illusions containing knowledge they themselves didn't have.
"Peter, you don't seem quite right. I suggest you go home and get a good night's rest. Come back another day."
Dr. Octavius frowned when the young man continued ignoring him. He was starting to think this guy might be unreliable.
If not for the personal recommendation of Harry Osborn, heir to Oscorp, Dr. Octavius would have already kicked him out of the lab.
Before Batman could respond, a sharp jolt stabbed the back of his neck. Like being pricked with an ice-cold needle, the chill instantly exploded, racing down his spine throughout his entire body.
The surrounding world seemed to freeze and stretch. Every tiny sound amplified: fabric rustling, equipment shifting slightly, even his own heartbeat...
Each sound suddenly magnified and distorted in his ears. The cold sensation in his chest pointed toward the Tokamak device, as if it were the source.
An alarm suddenly blared through the laboratory. The white lights switched to flashing red warning lights.
Dr. Octavius quickly turned to the control panel beside the Tokamak device, working the controls. Within two minutes, the laboratory lights returned to normal and the alarm ceased.
"As you can see, my fusion experiment isn't quite successful yet. I need to review the experimental procedure to see what went wrong."
Dr. Octavius smiled at Batman, showing no sign of frustration over the failure.
What experiment succeeded on the first try? Each failure gave him valuable experience. Dr. Octavius wasn't discouraged.
'That sensation seemed like an instinctive response to approaching danger...'
Batman looked at Dr. Octavius.
"Doctor, I'd like to borrow your computer."
He didn't explain his purpose. Dr. Octavius didn't particularly care either. He was busy checking through what had caused the experiment to fail, and readily agreed after hearing Batman's request:
"No problem."
With Dr. Octavius's permission, Batman immediately sat down at an idle computer. His hands flew across the keyboard.
Whether he was trapped in an illusion or something else had happened, gathering information on his current identity was the first priority. Batman immediately hacked into the local police system, searching for information on Peter Parker.
This included identity records, housing information, and school records.
"So this is my identity? A junior at Empire State University in New York. An orphan raised by his Uncle Ben's family since childhood?"
Batman exited the webpage expressionlessly, erasing all traces of his activity. He stood and bid Dr. Octavius farewell.
Based on the housing information in the New York police database, Batman walked for nearly an hour before reaching the apartment.
He locked the door, drew the curtains, and sat cross-legged in the living room with his eyes closed.
During the hour-long walk, the crowds and buildings had given Batman ninety-nine percent certainty this wasn't an illusion. But he needed to make one final attempt: meditation.
He'd learned meditation from Zatanna to resist mental attacks. It also had some effect against hallucinations.
Three full hours passed. Night had fallen. In the dark apartment, Batman's eyes suddenly opened.
"Not an illusion. But I can't rule out that Barry did something with the timeline, causing a chain reaction."
"I need to find out why my consciousness ended up in this unfamiliar young man's body. And I need to find a way back to Gotham."