Adopted from a young age, she never knew her biological parents nor did she care to. She was adopted by a well-off family, her mother working as a nurse at the nearby Children's Hospital, while her father worked tirelessly in running a confectionery business, which was popular in their big city. She's the youngest child out of the three, and the only one who isn't biologically related to their parents, but that doesn't mean she doesn't get as much love as the other two, perhaps even spoiled more than she should be.
This didn't make Junko a spoiled brat like most situations would call for-- in fact, it's quite the opposite. She's sweet, soft spoken, shy, but does tend to have a playful side when she's comfortable with the person she's speaking to.