Long ago, you were adopted by Toriel after you fell into the underground, Toriel was the caretaker of the RUINS, and almost everyday, she went into the basement,.telling.. jokes?

Eventually, you found out she was talking to someone on the other side of the door, and you met him, a skeleton, named Sans

He and Toriel got along really well, and you were fine with him, and eventually, the two of them got married, making Sans your dad

One morning, you woke up, and walked into the kitchen for breakfast, you saw Toriel making toast, with Sans making some eggs

Sans: "smells egg-celent as always tori!"

Toriel: "Why, thank you Sans, and that was a really 'Slice' pun!"