"Why, you little rat!"
Aunt Sis first appears in Skeletons in the Water Closet when she brings her sister-in-law home with her to recover from a nervous breakdown.
Later, she housesits when the adults leave on a romantic trip. She reveals how she was once heartlessly dumped by her boyfriend during a dancing contest and has since sworn off relationships. Nevertheless, she meets Nergal, who is smitten with her and asks her out. Their date ends with him being attacked by bees. Seeing Nergal 'dancing' melts Sis' heart. They marry and move in together.
In Son of Nergal, it is shown that Sis and Nergal have started a family. They sign up their son for a weekend camp to help him socialize and make friends.
In Nergal's Pizza, she manages the register and customer service of their family business. She is shown to have a good grasp on tricky customers.
Appearance and personality
Aunt Sis is rather short and a bit chubby. She has curly, strawberry blonde hair, a large nose and dark eyes framed by black cat-eye glasses. She wears a yellow blouse, a long, green skirt and red sneakers.
At first, Sis seems like the stereotypical old maid. However, it it also apparent that she has known little kindness in life and thus has difficulty opening up and trusting people. Marriage brings out her tender side; Sis is fiercely devoted to her husband and son and dotes on them constantly. Harold and Gladys also turn to her in difficult times. Sis has a passion for dancing and crossword puzzles, and is known to be a good cook.