Chapter 1: Unforeseen

It was a peaceful day in the underground. Monsters were laughing, playing, and living life to the fullest. The Royal Guard was having a feast, in celebration of the things they had achieved. Little did they know, humankind had prepared to make sure nothing remained of monster kind. For now, however, monsters were roaming, living like there was no care in the world. Arianna, a human who had fallen into the underground around two years before the incident, lived with the skeleton brothers. Within the skeletal household lived Fightale, Sans, and Papyrus.

"Good morning boys! I made some pancakes!" Arianna said enthusiastically. Sans stumbled over lazily and sat on the couch as Arianna handed him a plate. "Thanks, Ari, means a lot." Papyrus, on the other hand, rushed down the stairs, filled with hope for the new day awaiting him. He happily took a plate, then offered one to his oldest brother, Fightale. "No thanks, not hungry." He grumbled. "Aw c'mon, you gotta eat something!" Arianna stated as she tried to stress the importance of breakfast. "If not for yourself, then do it for me?" She then smiled brightly, trying to encourage him, which succeeded. "Fine, if it'll make you shut up." Fightale then took a plate and began to eat.

Meanwhile, in Hotlands, Undyne and Alphys were planning a date night together. Toriel had been invited as a special guest to help them pick out the destination and bring it all together. "Waterfalls is a rather nice place, perhaps you should bring your date there at some point." She said in a motherly tone. Undyne was more than happy to accept this recommendation from the queen, but Alphys was still a bit nervous about it. "What if something goes wrong?" She murmured. "Well then, you could just make fun of the situation at hand! Don't let one incident drag you down, dear." Alphys then smiles, feeling a bit relieved with that statement. "I will try my best!"

Later that day, Arianna was walking through Waterfalls with Sans, chatting about what to do later. She spotted Alphys and Undyne in short, pretty dresses walking their way and Arianna jumped up with excitement, "Alphys, Undyne, Hey!" She exclaimed. Sans waved and grinned as Undyne picked Alphys up and ran over to talk with the others. "Hey! What are you two punks doing? Dating?" Undyne teased. Sans just snickered, while Arianna huffed and crossed her arms. "I will have you know I am not dating Sans." "But you totally would!" Arianna paused, not wanting to lie, and she looked away and sighed. "Maybe I would, maybe not." Sans acted as if he paid no mind to this, although inside he was bubbling. "Yeah, 'dyne, we are just friends, ever heard of it?" Sans added. "Alright, alright, well Alphy and I here are on a date! Got any suggestions for where to go next?" Arianna perks up and smiles softly, "How about you go for a walk through the Snowdin forest! There sure are some pretty views there if you know where to look!" "Or you could go to Grillby's" Sans smirks while Arianna shoots him a glance.

Undyne and Alphys take Arianna's advice after wandering through Waterfalls, swimming, and eating at Mettaton's resort. Their feet crunch in the snow as they weave through the trees and the crisp wind breezes past them. They make it to a marvelous scene. Icicles were hanging from a cliff and a frozen waterfall with water barely trickling over the ice from the river. The light from the ceiling crystals beamed down onto the ice, making it glisten perfectly. The two then proceeded to a new location, ending up on the path that led to Snowdin town.

When they arrived, they noticed the Ruin doors slightly cracked open, and there was a mysterious gas leaking from it. The gas kicked up the snow and looked like a giant cloud. Due to this. Otherwise, it would be transparent. It reeked of a sulfur odor, with a hint of a potent smell like a lemon. "What is th-that?" Alphys asked as she felt her anxiety creeping up her spine. Something was wrong. Undyne walked towards the large, purple doors, wanting to see what was going on. Alphys wanted to hold her back, but once Undyne was onto something, there was no stopping her, and Alphys knew that. Groans echoed through the corridors of the Ruins, making both concerned. "Toriel?" Undyne hollered. She listened in, hoping for a normal response. When nothing responded, Undyne sighed, "Must be something leaking, better go check the lab." Undyne turned away to leave, but Alphys spotted something down the dark hallway. "U-Undyne." She whispered as she grabbed onto Undyne's arm.

Down the hallway was a monstrous goat, horns large, jaw hanging low, eyes blinded, and a hunched posture. Alphys covered her mouth in fear; whatever this gas had done to Toriel. "Toriel? What's wrong with-" Before Undyne could finish, a loud cry ripped through the air, and the monster bellowed out a plea for help. Alphys grabbed Undyne and tried to motion her to leave, but she did not. Instead, Undyne hurried down the hall, using the collar of her dress to cover her lower face. Toriel reached out with her large hands and smiled eerily. Undyne then tried to grab her, choking on the gases herself, but she did not give up. "Run." The monster growled out. "Run for your life." Their eyes locked as Alphys cried out for Undyne to hurry, and with that, Undyne went back, heading out of the doors. She made sure to close them so the gas would leak more slowly. "We have to warn the others about what is happening! I d-don't think anything in my lab could do that to a monster." "You're serious?" Undyne shuddered, knowing the whole underground population could be in potential danger. Alphys sadly nodded so Undyne picked her up and began to run to the lab. "We better get going then!"

Back in Snowdin, Arianna and Fightale were going to Fightale's training spot, where he shot his guns and tossed knives to practice his aim. "So, are you finally going to teach me how to throw an axe?" Arianna asked expectantly. "You think you're ready for it?" "Yeah! I can do anything if I put my mind to it!" "Sure you can." He smiles, secretly loving how positive Arianna is. Eventually, they arrived, and Arianna immediately went for the axe that was stuck in the wood, but no matter how hard she struggled, she couldn't pull it out. Fightale chuckled as he watched before finally helping her get it out, completing the task in one tug. Arianna thanked him before taking the axe from his hands, then tossing it towards a tree, missing the first try. She slumped, "Aw man…" Seeing her disappointment, Fightale decided to let down his guard and sighed. "Here, let me show you." The axe came flying to his hand as he used telekinesis to bring it to him, then he hauled it off and launched it into the air before striking the tree. Arianna smiled but still felt incompetent. Once he retrieved the axe once more, he took Arianna's hands and placed the axe in them. "Try again, you'll get it eventually." He assured her, smiling down into her blue eyes. Arianna nodded, appreciating his comforting words, as she pulled her hand back. Before she could let go of the axe, Fightale grabbed her arm, "No, do it from a different angle, maybe that will work better." He then positioned her, before letting her throw it. The axe landed right in the middle of the tree, and Arianna jumped up in joy. "I did it!" She cheered. Fightale laughed and nodded, before coming to a stop when Arianna hugged him. "Thank you, Fightale, it means a lot to me that you even try to put up with me messing up." He looked down at her and sighed, smiling softly, before hugging her back. "Anytime Ari."

Arianna went to grab the axe again when she noticed Fightale looking around. "Are you ok? You seem distracted." "Yeah," he mumbled, " I'm fine." She nods and walks back towards him with the axe before throwing it again, barely hitting it. She feels accomplished, then turns back for Fightale's approval. "Did you see…" Fightale wasn't paying attention, instead, he was looking straight into the middle of the forest. "Fightale," she tugs his sleeve, "are you sure you're fine?" He looks down at her, his face concerned. "Really, I'm fine, but… Do you smell that?" Arianna then takes a whiff of the cold, crisp air, trying to pick up on any different scents. Eventually, she picks up a tangy smell, like sewage water. "Ew, what is that smell?" She said in a revolted manner. "I don't know, but it's probably nothing." "You sure? Should we investigate?" "No no, it's probably ok, don't overthink it like you always do." She scoffs, playing around as if she was offended. "I do not overthink everything!" "Sure you don't." He smirks. She just smiles and giggles, enjoying the playful banter. "Now c'mon Ari, show me what you got."