Ayaka Shindō is a Spirit World Warrior who operates in Nagatsuki City, though her nature differs between source materials. In the original light novels she appears as a human, but in the anime adaptation she is a youmu, specifically one capable of manifesting as a powerful nine-tailed fox in times of crisis. She runs the Shindō Photography Studio, an establishment that functions as a dual-purpose space, serving as a café for ordinary, unsuspecting humans while also acting as her base for appraising youmu stones brought in by Spirit World Warriors. Her residence, which doubles as her appraisal office, is located in Nagatsuki City and is shared with her younger sister, Ai Shindō, a cat youmu who attends high school and helps manage the household duties.

Ayaka maintains an outward demeanor that is consistently calm, level-headed, and somewhat mysterious. This composed exterior, however, often gives way to a sharp and almost cruel sense of humor. She takes evident pleasure in teasing those around her, most notably by publicly sharing the embarrassing contents of postcards sent from Akihito Kanbara's mother, Yayoi, whom Ayaka has casually described as big-busted and kind of crazy. This playful, sometimes merciless teasing extends to others as well, as she has been known to intentionally omit details about a youmu's defensive mechanisms, such as spraying stinky liquids, simply to observe the reaction of Mirai Kuriyama. Despite this penchant for mockery, Ayaka is not unkind. In moments of genuine crisis, she reveals a serious and protective side. She is quick to reassure her sister, speaking softly to allay Ai's fears even when their home is surrounded by hostile youmu. She is also notably practical and money-minded, as shown when she prevents Akihito from photographing Mirai in a bunny outfit without proper payment.

Ayaka serves as a crucial link connecting Akihito Kanbara to the world of youmu and the Spirit World Warriors. One of her key functions in this role is activating and interpreting the specially crafted postcards that Akihito receives from his mother, Yayoi, often relaying their eccentric contents to him. As an appraiser, she holds a respected position within the local Spirit World Warrior society, using her extensive knowledge of youmu to assess the value of stones harvested from defeated creatures. She warmly accepts Mirai Kuriyama as a friend of Akihito's and remains fair and impartial when evaluating the youmu stones Mirai brings to her.

Her key relationships are defined by a few central figures. The most significant is with her younger sister, Ai. While Ayaka can be teasing with others, she is consistently kind, protective, and nurturing toward Ai, revealing a softer, familial side beneath her enigmatic persona. Her relationship with Akihito is built on her role as a mediator and information broker, connecting him to his mother and the spirit world, often to his embarrassment. She also engages in strategic dialogues with Hiroomi Nase, acting as a mediator who questions his methods and discusses the balance of power between the Nase clan and the youmu, showing that she holds high expectations for him.

Throughout the story, Ayaka demonstrates significant development, particularly in her willingness to engage directly in dangerous conflicts. Despite being a youmu herself, she has worked alongside the Spirit World Warriors of Nagatsuki City for at least three years. During the Calm, a phase that weakens most youmu, she displays surprising power by defending her sister and other weakened youmu against the attacks of Miroku Fujima. Later, she is absorbed into the massive youmu known as Beyond the Boundary. Rather than being destroyed, she survives and actively aids Akihito and Mirai in defeating the hostile entities within the gigantic youmu. In the sequel film, she confronts Izumi Nase, who has been possessed by a parasitic youmu, and is thrown into a building during the fight, yet she survives and contributes to subduing Izumi.

Ayaka possesses several notable abilities. She is highly knowledgeable about youmu, their behaviors, and their worth, which is why the local Spirit World Warriors hold her in high esteem. She is an expert in barriercraft, capable of constructing potent barriers for various purposes. One such barrier is used to ward off ordinary humans, ensuring that only Spirit World Warriors can access her studio. Another barrier takes the form of a giant dome that can expand and annihilate multiple youmu simultaneously. Her most formidable power is her youmu transformation into a large, white nine-tailed fox. In this form, she retains significant power even during the Calm, when other youmu are weakened. She can project powerful energy blasts from her mouth and erect protective shields, making her a formidable combatant despite her typically calm and reserved nature.