Hikari Nakazato is a supporting character known for her vibrant and energetic presence. She is the cousin of the main protagonist, Kenji Tomosaka, and is one year older than him, though her youthful appearance often leads others to mistake her for being younger. She has a small stature, standing notably short, with light brown hair typically styled into twin tails that complement her active and spirited demeanor. Her birthday, blood type, and detailed measurements are a matter of record, reflecting her characterization as a petite individual with a slim figure.

Her personality is defined by a quick-tempered, tomboyish nature that makes her both endearing and exhausting to those around her. She is a natural actionist, preferring to do what she wants without hesitation, and if she believes something is fun, she will charge into reckless situations that often defy common sense. This free-spirited approach to life means she frequently clashes with Kenji, their daily arguments and physical squabbles serving as a primary source of comedic relief. Despite this chaotic energy and her tendency to be a nuisance, she possesses a strong undercurrent of loyalty and care. She is genuinely concerned for her cousins and her close friend Nanami Konoe, willing to help them when they encounter real trouble.

Hikari serves a specific role as a catalyst for interaction among the main cast. Because her school vacations start earlier than those of the rural town where Kenji lives, she often arrives as a herald of summer, injecting city-born energy into the countryside setting. Her mischievous nature frequently pushes Kenji and Nanami closer together, acting as an instigator for their romantic development even while causing chaos for her own amusement. She has a notable fondness for extremely spicy food, a quirk that renders her home cooking nearly inedible to others, as well as a preference for milk and carbonated drinks.

Key relationships define her interactions throughout the narrative. Her dynamic with Kenji is characterized by constant bickering and playful violence, a testament to their long familiarity as cousins who grew up playing together before Kenji moved away. She also shares a close friendship with Nanami, having grown attached to her during summer visits. Much of her time in town is spent with these two, creating a familiar trio dynamic. She also attracts the obsessive attention of Kenji's friend, Hatano, who is captivated by her. She is aware of his infatuation and tends to take advantage of his willingness to serve her, treating him more like a plaything than a serious romantic interest. While some accounts suggest a hidden stubborn affection for Hatano, other detailed sources focus primarily on her teasing and self-serving treatment of him.

In terms of development, Hikari remains a consistently energetic and disruptive force. Her character does not undergo a dramatic personality shift but rather serves as a stable, vibrant backdrop that highlights the quieter growth of other characters. Her primary motivation is a simple one: to enjoy her vacation to the fullest, which for her means stirring up excitement and dragging Kenji into adventures. A notable ability is her extreme palate, which allows her to consume intensely spicy or sweet foods that would deter anyone else. Physically, she is surprisingly athletic for her small size, and her unyielding energy allows her to perform feats like leaping onto a sleeping person to wake them up. Her childish appearance contrasts sharply with her position as the oldest among the heroines, a fact she occasionally tries to assert, though her behavior consistently undermines any authority her age might grant her.