Nana's sister is depicted as a somewhat short young girl with a simple bob cut. As the manga is mostly in black-and-white, including both of the panels she appears in, it is difficult to determine her hair color. However, its shading is almost identical to that of her older sister and it is within the realm of reason to posit that they may have similar hair colors in actuality. In her sole appearance, she is drawn wearing a light-colored, collared, button-down shirt with short sleeves tucked into a modest dark-colored skirt.
Nana's sister gives the impression of being surprisingly mature and dutiful for her age, encouraging Nana to persevere and learn to work with Friends of different personalities in her capacity as caretaker, with the (quite adult) rationale that "it's her job to do so". She does not seem particularly sympathetic to her big sister's situation in the sole chapter we see her in, addressing Nana with a gentle yet detached smile, although with such a short introduction to her character it's difficult to draw any lasting conclusions about the nature of their relationship from this. It is however of note that Nana has no reservation sharing her frustrations with her, suggesting some level of familial warmth.
Role in the Plot
Volume 1, Chapter 1
The sister makes her sole appearance after Nana returns home from her first day on the job, visibly exhausted thanks to Ezo Red Fox's disobedient antics. She asks about Nana's day (whilst informing her that she needs to take her bath soon, as it's about time to turn off the lights in their household), to which the latter describes her stressful relationship with the aforementioned fox Friend. Unfazed, the sister comments that, while it seems like working with her will be a little difficult, managing personalities like those is Nana's job. She tells her big sister to do her best, to which Nana responds "Easier said than done...", ending the short scene. This is the first and last appearance of the mysterious sister character, and to date her name is unknown.