Shouko Kubo is the younger sister of Masaru Kubo and a childhood friend of Yukinojou Yukimura. She possesses blue eyes and long blue hair, frequently styled with spiky bangs, wavy sections, and twin tails. Standing at 153 cm tall, she has a slim build and pale complexion.

Shouko managed her brother's boxing club despite her personal aversion to the sport. Witnessing Masaru and Yukinojou fight each other caused her deep unease due to her close bonds with both. After an accident left Masaru comatose, she harshly blamed Yukinojou for the incident. Unable to bear her condemnation, Yukinojou relocated to Kashima city. Shouko followed him there, resolved to prevent him from evading accountability for the tragedy.

Her personality blends kindness, protectiveness, and intelligence with a reserved, shy demeanor. She enjoys nature and maintains a generally relaxed attitude, though her pursuit of Yukinojou exposes persistent, unresolved anger beneath her calm exterior. Despite this resentment, she retains underlying empathy and a fundamentally compassionate nature.

In daily life, Shouko is practical and domestically inclined, often cooking and cleaning. She typically wears school uniforms, skirts, turtleneck sweaters, and aprons, accessorizing with ribbon hair ties. Her relationship with Masaru reflects deep sisterly affection and concern, while her dynamic with Yukinojou remains strained by past trauma and her unresolved quest for closure.