A/N: Baron is Undyne's brother, and neither of them know if the other is older. Baron is more withdrawn than Undyne when the characters meet them later, and while his fighting skills are impeccable, he reveals later that he doesn't really like to fight anymore, and really only does it for his sister.

"Baron, come on! I wanna practice, you said you'd practice with me an hour ago!" Undyne growled, planting her foot firmly on her brother's lap. He glared up at her, yellow eyes narrowing.

"Leave me alone," He said, shoving her foot off his lap. "I don't wanna practice right now, the new episode of Mew Mew Kissy Cutie is on and you already made me miss last week's!"

"Ugh, you are SUCH a weeb. Why don't you just marry Alphys and get it over with and you can be stupid happy weebs together?"

"One, because we're ten, and two, I don't even like Alphys, YOU do!" Baron said, sticking his tongue out in punctuation. He returned his attention to the TV and bobbed his head along to the theme song, ignoring his sister's flushing face.

"I-I SO do not!" She trudged across the room and grabbed her spear, quickly hurling it across the room at her sibling. Baron caught it without even looking away from the TV and threw it on the floor next to him.

"Mom won't like you throwing your spear in the house," he muttered.

"Mom won't like your FACE in the house!"

Baron looked over at her with one eyebrow raised. "That doesn't even make sense, Dy."

"Ugh! You're so annoying! Fine, I'll go find that skeleton kid I met the other day and practice with him instead!" She collected her spear from the floor and took a step before Baron grabbed the hem of her shirt, sighing.

"Okay, okay, I'll practice with you, but...you owe me one episode! You gotta watch with me next time."

"Ugh, why can't I have a cool brother?"

The spear landed too close for comfort, nearly nicking her skin. Undyne looked for an escape route. C'mon, Dy, think!

She cast her eyes to the left: Blocked off by spears.

To the right: Fallen trees.

"What's the matter? Can't get away?"

She snapped back to the battle at hand, eyeing her brother suspiciously as he stood on the tip of a spear embedded in the ground, his trusty scepter glinting in his hand. It had been harder and harder to beat him in their brawls lately, and ever since he'd turned sixteen and taken an interest in the Royal Guard, he'd been merciless. She couldn't help but wonder if he had been going easy on her all this time, and only just found his motivation.

She also couldn't help but be excited for the challenge.

"Heh, Escape? Which sister are you thinking about, nerd?" She summoned a blue spear to her hand and hurled it at him, hitting only air as he quickly phased away. "C'mon, Weeb! Hit me for real instead of running away!"

"As you wish!" The strike hit her stomach, and Baron grinned up at her as he grabbed her hand, stopping her from summoning another spear. He tapped her nostrils with his scepter. "Boop! I win!"

She groaned as he released her hand. She'd never lost at practice, at least not to Baron. She collapsed onto a nearby rock, glaring up at her brother's smug face.

"Jeez, when did you get so fast? And since when do you have so much motivation to…" She trailed off as realisation hit her. "Oh my lanta, this is about Brys isn't it?"

Her brother's face said it all as the smug look was wiped off, replaced with a shocked one. "I-it's so not!" He dug his scepter in the ground and turned away so she couldn't see him blush.

"It SO is! Just the other day he said he thought the Royal Guards were the coolest and he admired them a lot, and now suddenly you're all gung ho about joining! You're trying to impress him!"

"Sh-shut up! I'm missing my shows, leave me alone!" He pulled his hood up to cover his face.

She watched him rush away, and chuckled at his panic. Her brother was such a cinnamon roll, he would never last in the Royal Guard. Luckily she was there to protect him.

The only thing he felt was the rage in his heart subsiding slowly. The human, the one with the gun...the one that had hurt his sister…

He snapped back to reality to the sound of coughing. He looked down at the human at his feet, shakily pointing his gun at him.

"Are you going to shoot me?" Baron scoffed, his voice dark and foreign. He knocked the gun out of the boy's hand and slammed his scepter inches from his face. "Are you going to shoot me, like you did my sister? Is that the plan?"

He aimed his scepter at the boy's chest. Who was he anymore? This wasn't who he was, it wasn't how he did things. But he couldn't stop himself. The scepter shot the human's soul with a crack.

"Three monsters dead." Crack. "My sister blinded." Crack. "Attempted murder of the king."

The boy shouted as Baron pinned his arm to the ground, preventing him from reaching his gun. The human went limp and looked up at him, eyes saying all that he could not.

"Mercy, huh?" Baron stepped back, swinging his scepter back to rest on his shoulder. "I'm inclined to agree on normal terms, but…"

His lips tightened. Don't do this, he thought. This human was...just a child. He shook the thought away. This child had killed his fellow guards and wounded his sister. He felt the rage in his chest again, and subsided to the cold feeling once more.

"Listen, kid. I gotta job to do, so just hold still, ok?"

The red mantle was placed on his shoulders, a prize for bringing a precious human soul for the gate. The king gave him many praises, and monsters all over thanked him for stopping the murderer. Even Undyne was impressed, and didn't notice he couldn't look at her eyepatch without feeling sick.

Life became easy, and as the captain he had many troops at his disposal. The next time a human came, he didn't even have to see them. Lady monsters sighed as he passed, men whistled and cheered. Brys even smiled more when he saw him.

Everything should have been perfect.

Everything should have been exactly what he wanted.

He should be happy.

But when Baron looked in the mirror, all he could see was a murderer.

A/N: There wasn't as much backstory to Baron as I originally wanted, so I may expand on this later. I have pictures of all my underkin characters on my Deviantart: Gracie11facie