Sayaka Koyanagi’s personality is deeply shaped by a past marked by emotional turmoil and betrayal. She was once in love with a female teacher, but their relationship was fraught with moral doubts. Sayaka confided in a friend about her feelings, only for the friend to betray her trust by publicly revealing the secret. This devastating betrayal led to the teacher’s suicide, leaving Sayaka with a deep sense of loss and distrust.

As a result, Sayaka developed significant trust issues, becoming wary of others and highly guarded in her relationships. Her experiences made her resolute in defining her own path, leading her to form a group of Collectors with a clear, singular goal, gathering the hundred coins. Her ability, which she received later, reflects this sharp determination and desire for control, born out of the emotional scars left by her past.

Sayaka Koyanagi is a young girl with bra-length black hair, featuring square bangs that fall neatly over her forehead. She has striking blue eyes that stand out against her dark hair.

Her usual attire includes a swimsuit top paired with short pants, long gloves with sleeves, and a collar adorned with a plus symbol, giving her a distinctive, battle-ready look. To conceal her identity, she wears a hockey mask, which adds a layer of mystery and anonymity to her character. Underneath her outfit, she wears a G-string panty, completing her unique and striking appearance.

Sayaka Koyanagi’s ability is a reflection of her intense determination and need for control over others. She possesses the power to force individuals who make contracts with her to keep secrets, whether it’s her own or those of her friends. To activate this ability, Sayaka ties a string of her hair around the person’s neck. The string soon becomes invisible and essentially merges with their body, making it undetectable to others.

If the person betrays her trust and reveals any of the secrets they were sworn to protect, the string tightens, gradually constricting around their neck. If the secret is divulged, the tightening becomes lethal, ultimately killing the individual. This deadly consequence ensures that those who enter into a contract with Sayaka remain loyal to her and her interests.

The first name “Sayaka” is composed of the kanji 紗 (sa), meaning “thread” or “silk,” 耶 (ya), which can be interpreted as a question mark or a particle that adds emphasis, and 香 (ka), meaning “fragrance” or “fragrant.” The combination of these kanji evokes a sense of delicate beauty and a subtle, yet powerful presence, fitting for Sayaka’s enigmatic and forceful nature.

Sayaka’s surname, “Koyanagi,” is made up of the kanji 小 (ko), meaning “small,” and 柳 (yanagi), meaning “willow.” The name suggests a connection to nature, particularly the graceful willow tree, while “small” could imply a sense of fragility or subtle strength, much like the character herself.

The surname Koyanagi is most commonly found in eastern Japan, with some families pronouncing it as “Oyanagi.”