Okay, so I really like the idea that Grillby has PTSD from fighting in the human/monster war. I will warn you now, this will most likely be shit, so I apologize in advance.
The last few people filed out of the building, biding Grillby farewell as they all dispersed, heading for their homes. Glancing at the sky as he closed the doors, the bartender noticed dark clouds rolling in at an alarming rate, the air smelling of oncoming rain. He sighed, realizing he had forgotten his umbrella at home. Dissapointed at the thought of having to spend the night waiting the storm out at the restraunt, he went about cleaning the place up, the quiet patter of rain just beginning.
He was just polishing the last glass behind the bar as the first clap of thunder shook the building. The object fell from his hands, shattering as memories filled the his mind.
Burning. Everything was burning. Cannons were booming and and the sound of gunfire filled the air. Humans were screaming as their town was being destroyed, their loved ones being murdered in front of them. The flame monster stood atop a hill, watching. He gave the command, and more troops marched towards the chaos. He didn't even flinch.
Grillby had fallen to his knees, his hands placed upon the floor as if to keep him from collapsing. They left scorch marks in the wood, but he didn't notice. He let out a sob. He hadn't realized that a certain skeleton had walked in, hearing the faint sound of glass shattering from outside.
At first, Sans didn't see his friend, but quickly rushed to his aid when he heard the sob from behind the bar.
"Hey, Grillbz, you okay?" He asked, placing a hand on his shoulder. Grillby flinched at his touch, immediately swinging his fist. He was once again consumed by memories, and he believed he was still on the battlefield. To him, Sans was a threat.
The skeleton had dodged just in time, but wasn't fast enough when a bottle was hurled at his head. It left him seeing stars, and he fell on his back.
Grillby picked up a chair and threw it, watching it smash against the wall above Sans' head.
He watched as innocent men, women, and chilren lost their lives because of him. A human soldier looked up at him from the ground, badly injured. The man pleaded for mercy, but flames consumed him before he could utter another word. Grillby watched as the skin and muscle melted off the soldier's body, his screams of pain still echoing in his head.
Grillby had fallen a second time, curling up into a ball on the floor. Sans kept his distance, afraid of what his friend was going to do next. All the bartender did was sob, desperate to escape the ghosts of his past.
This time, he didn't flinch as Sans wrapped his arms around him, holding him close and whispering over and over that it was going to be alright, that it was over now. That he was safe, and nothing that happened in the past mattered.
It was hours after the storm stopped when Grillby finally calmed down. Every flash of lightening and every boom of thunder had set the bartender off again, filling him with pain and despair. The entire time, Sans had refused to leave his friend's side, and he had sat with him until morning.
Eventually, Grillby had drifted into sleep, head resting on the skeleton's shoulder. He had tired himself out with everything he had done that night. Sans just continuted to whisper encouraging things to the man, even after his crying had stopped and his breathing had slowed.
The shorter monster took his blue hoodie off, draping it over Grillby as he slept on.
