He got to the barrier while walking through the dust, and dead bodies of all the monsters and humans that died during the fight.
"Well, looks like this is the time that a monster finally leaves the underground. *sigh* Let's go guys." He steps through the barrier and felt the magical properties of it affecting his very soul. His ears began to ring, when he opened his eyes to see the surface, it was night, smoke bellowed from the factories and covered the night sky. Someone began to drive past him in a black van. He jumps into the bushes making sure no one sees him.
"Well boss it looks like they're all dead." An unknown voice was talking through a earpiece he had.
"Who the hell is this guy?" Sans was now wondering if this guy was working for someone.
"Huh? What was that, who's there?"
"Crap!" Sans ran out of the bushes and towards the van, then he knocked out the driver and hopped in the car, and drove off.
"HEY COME BACK HERE!" Sans heard the person behind him scream at him before he was out of earshot.
"That was a close one"
Sans noticed a map showing an odd route
"Let's see where this guy was going."
He pulled up to what seemed to be an abandoned building and entered
"Get him!" Yelled a man in the building
Then, gunshot. But Sans just stood there laughing. Then, the firing ceased.
"How are you still alive?" Asked the man
"Hehe, Bullet proof vest, or maybe it's just my thick skull."
Then Sans took out his machine guns and began rapid firing until all sound stopped.
"So, you found me… good job numbskull"
Said a familiar voice behind him.
Sans whipped around and began to fire full blast at the figure but then they vanished.
"It's not gonna be that easy this time Sansy."
The figure said from behind him
"You see, I found the more souls I take, the more powerful I am. So I've been doing my fair share of killing."
Sans couldn't believe what he was hearing
"K-kid, What happened to the old you? I remember who you were before all of this… what happened?"
He asked trembling
"You'll find out soon enough, until then I'll see you around."
The figure said before vanishing.
Sans stood silent in the building, his trench coat swaying in the wind, everything had changed.