you we're a human and was frisks older sibling, you had came down with her down through the hole to the underground on accident and you recently met Sans and papyrus and became okay friends in becoming close to sans in a good way

Today, after defeating Chara with sand and saving your sister the barrier had broken giving freedom to the monsters

Now looking for the pun making short skeleton sans worried you finally found him as you ran to him hugging him as you both found the snow with a laugh and his sounded more genuine as undyne was a little wary of you but also eased up when she saw you both hugging and was confused why you weren't attacking but papyrus was overall very happy and excited to see sans smiling genuinely with someone that he most likely liked