For this fanfic I'm going to use glitchtale gaster, undertale grillby, and undertale asgore. Hope you enjoy!
Chapter 1: Gaster
Gaster came rushing into the throne room shouting "My lord!, Your son has been killed by the humans!" Asgore then dropped the water he'd been using to water his flowers. Asgore then spoke "Are you sure he's dead?". " I'm afraid so..." answered Gaster. "Give me some time to consider my options" said asgore. Gaster quietly left the room but before he closed the door he could hear sniffling and something being thrown. As Gaster headed back to his house he was greeted with a young Papyrus. " Hi Gaster!" Papyrus shouted with a joyful tone. " Hello papyrus". "Where is your brother?" Asked gaster. Papyrus then pointed to San's room where Gaster could hear very loud snoring. "Good" Gaster whispered. As he made his way down the stairs to his lab he noticed a note on the door. It read " We need to talk." And it was signed by grillby, an old friend of his. Gaster made his way upstairs and grabbed his coat. As he opened the door he thought of Sans and Papyrus being killed by the humans. One of his eyes started glowing orange, Papyrus noticed this and asked " Dad, where are you going?" Gaster's eye faded and he turned to papyrus. "I won't be gone long, now take care of your brother got it?". Papyrus then saluted to gaster and gaster smiled. He closed the door behind him and started walking through the falling snow. He saw Grillby's place and politely knocked on the door. Grillby opened the door and said "Come in". Gaster came inside and hung his coat on the coat rack. Grillby gave him a cup of coffee. Gaster then spoke " What did you need to talk about?". Grillby then stared out his window. "I heard about what happened to Asgore's kid" said Grillby. " Yeah, the kings thinking about what to do next" said Gaster. Grillby then looked at a photo of him and his wife. " Gaster, I'm gonna have a child in a couple of days.". "Congratulations!" Said Gaster. Gaster suddenly felt a vibration from his pocket. He picked up his phone to see a text from Asgore. It read "Come quick." Gaster then told Grillby that he had to leave. Grillby asked if he could come with him. "fine" said Gaster. They grabbed their coats and started walking toward the castle against the violently falling snow.
End of Chapter: 1