"Why, you little rat!"- Sis
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 arrives at Billy's home when the adults leave on a romantic trip. It is revealed that Sis was once heartlessly dumped by her boyfriend during a dancing contest. In the meantime, she catches the eye of Nergal. He is smitten with her and decides to ask her out. Their date ends with Nergal being attacked by bees. Impressed with his range of dance moves, Sis finally opens her heart to him. She accepts his marriage proposal and comes home with him.
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 handling tricky customers.
Sis is finally seen on a picnic with her husband and son. Beside the usual mishaps that come with being married to Nergal, she is content and in good health.
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 large, cat-eye glasses. She wears a yellow blouse, a long, green skirt and red sneakers.
At first sight, Sis seems like the stereotypical old maid. However, prior to meeting Nergal, it's apparent that she has known little kindness in life and has difficulty opening up and trusting people. While she remains a very private person, Sis is fiercely devoted to her husband and son and dotes on them constantly. She spends most of her time doing household tasks and enjoying her crossword puzzles.