Kotoko is a young woman with a petite build and doll-like appearance, often mistaken as a young child instead. She has fair skin and purple eyes framed by short, curly blond hair. As a Goddess of Wisdom, she also has only one eye and one leg, with her right eye and left leg being prosthetics. Her glass eye looks identical to her functioning eye, and her prosthetic leg attaches around mid-thigh height.
Her everyday outfit consists of a white hat with a black ribbon, a white dress with dark blue accents, white socks, brown shoes, and a red cane. The top part of her dress has puffy sleeves and can be taken off independently from the rest of her dress.
After the first arc, she alternates between different dresses.
She has a very outgoing personality and always makes an effort to find the root of any problem, especially when she has the help of yokai. She is oblivious to danger and she tends to be very clingy when it comes to Kuro.
Kotoko is a self-centered, unrepentant prankster, who enjoys poking fun at others expense, and is also a bit of a pervert. She is also shown to have a rather childish demeanor whenever she feels she is not given enough attention or proper treatment, which is aimed especially at Kuro, to whom she can be very pushy.
Contrasting with her mischief belies a cunning individual, well worth her epithet of "Goddess of Wisdom", demonstrating a calculating intelligence that borders in almost diabolical precision and frightening acute. Although she is a terrible liar to her peers, she is a highly manipulative, convincing liar while at work, being able to fool both ancient yokai and a multitude of online fanatics with terrifying accuracy.
At the young age of 11, Kotoko Iwanaga was abducted by yokai for two weeks and asked to become their "God of Wisdom," a mediator between the spirit and human worlds, to which the girl quickly agreed but at the cost of her right eye and left leg. After what happened, whenever yokai wish for their problems to be solved, they make their way to Kotoko for consultation.
She was discovered with "her left leg amputated and her right eye carved out."
Goddess of Wisdom: Kotoko becomes the goddess of wisdom after trading her right eye and left leg for the yokai that abducted her when she was a child. As a result, she is obeyed by most of spectres, though there are ones that disobey her. The yokai and spectres frequently ask Kotoko to solve their problem. In exchange, she often asks them about details of a case she handles, mostly if they are witness to the case. Additionally, under her order, she has shown to be able to send the spectres and yokai for various purpose, such spying and/or following other people.
Deduction: Kotoko is certainly intelligent and possesses incredible deduction abilities, able to solve supernatural cases. However, what's more impressive is her creativity to make more explanations if one theory can't satisfy her client. For example the Guardian Serpent, who is obsessed for an ideal answer, Kotoko eventually manages to convince him. As someone who's quick on her feet and always ready with a clever response, Kotoko mostly knows the right thing to say. Kotoko has also involved with what appears to be "dueling fictions" against Rikka Sakuragawa, effectively driving mass amount of people into changing their mind, and thus made the imaginary monster disappear.
Kuro Sakuragawa: They are currently in a relationship with each other. Kotoko met Kuro, who was 20 years old at the time, at the hospital when she was 15 years old. She fell in love with him at first sight. They meet again after two years at the same hospital just after Saki broke up with Kuro. Kotoko is pushy, clingy, attention seeking and many time selfish towards Kuro, causing the latter to be annoyed by her regularly. Despite her mischief, Kotoko genuinely cares for Kuro's wellbeing and does truly love him as a person and would rather he opened himself more. Although aware of Kuro's immortality, she still showed concern for him, as she repudiated the idea of Kuro being mauled and maimed repeatedly by Steel Lady Nanase in order to defeat her, and tried her best to defeat her quickly so as to not prolong the brutality of his fight.
Saki Yumihara: The two don't get along at first but eventually put aside their differences to solve the mystery of Steel Lady Nanase.
Rikka Sakuragawa: When they first met, Rikka told Kuro that Kotoko wasn't "a good one," only getting him to agree with her. After the awkward introduction, however, they became close and Kotoko even began visiting her at the hospital too.
- Her cat cane is custom made and although she doesn't need it, her family insists she uses it
- Her full name containts characters that each can be read as: "gan" from (ganseki) rock; "ei" from (eien) eternity; "koto" a Japanese musical instrument; and "ko" from child.
- During the showdown against Rikka Sakuragawa, Kotoko uses the username "kuebiko", which is the Shinto god of knowledge and agriculture, depicted in Japanese mythology as a scarecrow who cannot walk but has comprehensive awareness.