Big Sister Sho is a recurring character who appears as the older sister of Shimarisu, the chipmunk. Her full name, as presented in some sources, is Shou, and she is depicted as a rough and domineering figure within the forest community. Her primary role in the story is that of an antagonist to her younger brother, frequently visiting his home not for friendly sibling bonding but to assert control and cause chaos. She is known for her unreasonable behavior, which includes throwing away Shimarisu's treasured possessions, physically hitting him, and bullying him to the point where he is often forced to run away from his own home.

Personality-wise, Big Sister Sho embodies a classic bully archetype. She is aggressive, demanding, and seems to derive enjoyment from tormenting her brother. Her actions are driven by a desire for control and entertainment at the expense of others, showing little regard for Shimarisu's feelings or personal space. This behavior is so extreme that it once prompted Shimarisu to challenge her to a duel, a testament to his deep frustration with her tyranny. The stakes of this particular duel were characteristically high: if Shimarisu won, Sho would stop bullying him; if Sho won, he would have to obey her every command forever. Her bullying nature extends beyond her family, as innocent bystanders like the young sea otter Bonobono can also get drawn into her disruptive games.

The central and most defining relationship for Big Sister Sho is with her brother, Shimarisu. Their dynamic is entirely defined by her bullying and his attempts, usually futile, to escape or defy her. Despite her harsh treatment, the narrative also hints at a more complex family bond. In one instance, Sho has been away from home for a while, leading to a situation where Chipmunk is sent to find her. While he is unmotivated to search due to her bullying, this suggests that she is a member of the family who is missed or whose whereabouts are a concern, adding a layer beyond simple antagonism. She has also been shown to interact with other adult characters, such as getting into a conflict with Raccoon's Dad, indicating that her combative nature is not reserved solely for her younger sibling.

In terms of development, Big Sister Sho does not undergo a significant transformation; she remains a consistently forceful and troublesome presence. Her motivations are straightforward and do not evolve, as she continues to appear primarily to disrupt Shimarisu's life. She possesses no notable supernatural or special abilities, with her power stemming entirely from her forceful personality and the implied authority of being the older sibling, which she wields mercilessly to dominate Shimarisu and those around him.