Inside the DOM:
"It doesn't matter!" said a man's voice. "There are other ways in —WE'VE GOT THEM, THEY'RE HERE!"
Harry spun around. They were back in the Brain Room and, sure enough, there were doors all around the walls. He could hear footsteps in the hall behind them as more Death Eaters came running to join the first.
"Luna — Neville — help me!"
The three of them tore around the room, sealing the doors as they went: Harry crashed into a table and rolled over the top of it in his haste to reach the next door.
"Colloportus!"
There were footsteps running along behind the doors; every now and then another heavy body would launch itself against one, so it creaked and shuddered. Luna and Neville were bewitching the doors along the opposite wall — then, as Harry reached the very top of the
room, he heard Luna cry, "Collo — aaaaaaaaargh . . ."
He turned in time to see her flying through the air. Five Death Eaters were surging into the room through the door she had not reached in time; Luna hit a desk, slid over its surface and onto the floor on the other side where she lay sprawled, as still as Hermione.
"Get Potter!" shrieked Bellatrix, and she ran at him. He dodged her and sprinted back up the room; he was safe as long as they thought they might hit the prophecy —
"Hey!" said Ron, who had staggered to his feet and was now tottering drunkenly toward Harry, giggling. "Hey, Harry, there are brains in here, ha ha ha, isn't that weird, Harry?"
"Ron, get out of the way, get down —"
But Ron had already pointed his wand at the tank.
"Honest, Harry, they're brains — look — Accio Brain!"
The scene seemed momentarily frozen. Harry, Ginny, and Neville and each of the Death Eaters stopped in spite of themselves to watch the top of the tank as a brain burst from the green liquid like a leaping fish. For a moment it seemed suspended in midair, then it soared
toward Ron, spinning as it came, and what looked like ribbons of moving images flew from it, unravelling like rolls of film —
"Ha ha ha, Harry, look at it —" said Ron, watching it disgorge its gaudy innards. "Harry, come and touch it, bet it's weird —"
"RON, NO!"
Harry did not know what would happen if Ron touched the tentacles of thought now flying behind the brain, but he was sure it would not be anything good. He darted forward but Ron had already caught the brain in his outstretched hands.
The moment they made contact with his skin, the tentacles began wrapping themselves around Ron's arms like ropes.
"Harry, look what's happen — no — no, I don't like it — no, stop — stop —"
But the thin ribbons were spinning around Ron's chest now. He tugged and tore at them as the brain was pulled tight against him like an octopus's body.
"Diffindo!" yelled Harry, trying to sever the feelers wrapping themselves tightly around Ron before his eyes, but they would not break. Ron fell over, still thrashing against his bonds as the tentacles completely ensnared Ron's head underneath them...
It was at that exact moment an accident happened.
There was no way for anyone to know why it happened... Maybe it was because of the numerous broken time turners wreaking havoc in the surroundings... or maybe it was just the magically charged atmosphere or maybe it was something else entirely but suddenly in that exact moment everyone and everything in that room... froze.
From the death eater's malevolent gazes to the panic in the eyes of the teenagers, from the floating dust particles to the spell fizzling through the air, everything was frozen in time.
It was as if the room had been completely isolated in a different dimension where time had completely stopped. And amidst the frozen chaos in the middle of that room, a tiny crack appeared in the space... an unusually stable crack.
The crack was only there for about a nanosecond before disappearing. But that minuscule amount of time was enough for an invisible little soul to escape from the crack straight into the suspended chaos in the room.
The little soul was unconscious, but... not completely.
It was as unconscious as a plant and, just like a plant knew where to send its roots to survive, the soul too knew what it had to do to survive.
The soul moved through the frozen air, unbothered by any obstacles in its path, towards the only empty space where it could reside and survive, towards—the closest tentacled brain.
But the soul didn't find the cosy little home it was looking for in there... because the brain as it turns out, wasn't actually made to house a soul (well, at least not a human one) so sadly it was immediately expelled through the feelers... straight into the red-haired human in its grasp.
But the soul didn't leave the tentacled brain empty-handed.
The soul was a cheap stake in his previous life, the kind who couldn't stay in a fancy hotel and resist grabbing a few free towels along as souvenirs. And that ingrained habit worked its magic here too... and it grabbed something miraculous from the brain, something out of this world.
The souvenir it took from the tentacled brain was something that came from a much higher dimension.
It was a system, a one-of-a-kind artificial intelligence made by a higher lifeform for their own use... and sadly it had been left to rot in this brain ever since it was fished out of The Veil by the Unspeakables, who weren't smart enough to understand its mysteries. But finally, this miraculous system got the chance to boot up again... in the brain of one Ronald Weasley.
 [GAMER SYSTEM INITIALIZING...]
 [BOOTING...]
 [BOOTING...]
 [ERROR S9009: WORLD INCOMPATIBLE]
 [ERROR #@##$...]
 [SEARCHING...]
 [SOLUTION FOUND: FOLLOW PROTOCOL LIZARD]
 [REMOVING UNESSENTIAL COMPONENTS]
 [REMOVING INVENTORY...]
 [REMOVING DUNGEON SKILL...]
[DISCARDING REWARDS...]
[DISCARDING SYSTEM STORE...]
 [...]
 [GAMER SYSTEM DOWNGRADING...]
 [MAGE SUBSYSTEM RETAINED...DISCARDING THE REST]
 [FINALIZING...]
 [WELCOME HOST—]
 [NEW ERROR DETECTED!!]
 [ERROR 201: FOUND TWO INDIVIDUAL HOSTS]
 [SEARCHING...]
 [SOLUTION FOUND: FOLLOWING PROTOCOL X101]
 [SOUL CHECK...]
 [SOULS COMPATIBLE]
 [PERFORMING EMERGENCY SURGERY...]
After unexpectedly finding two souls in the brain of the red-haired human it had inhabited, The Gamer System—No, the Mage System, decided to... merge them.
It acted not unlike an overworked housewife, who after not finding the desired vegetables in the refrigerator, decided to just mash up everything available and call it a new dish.
The new dish or the new soul would have both the memories and the qualities of Ron Weasley from this Wizarding world and the wandering soul of Sam from the modern world.
Now, as for who was Sam, and how he came to be in this room in the DOM? Well... to know that we need to go back a few...