| This page may contain spoilers. Please view at your own risk.
Nayuki is Yuichi's cousin, as her mother was Yuichi's mother's younger sister. As a child, the two often played with each other, as Yuuichi frequently visited her town.
7 years prior to the beginning of Kanon, Nayuki confessed her feelings to Yuichi (in Japan, marriage between first cousins is legal). However, overcome with the shock after witnessing Ayu's accident, he became distraught and seemingly ignored Nayuki's words, and that left Nayuki heartbroken. However, deep down inside her, she still harbored hope for herself that one day, he would accept her.
In the beginning of Kanon, she is the one who arrived to greet Yuichi when he arrived to her town because of some circumstances, although she was late and Yuichi had to wait for hours under heavy snow. She was somewhat relieved when she saw Yuichi still remembering her name.
During both the Visual Novel and anime, Nayuki is often the one who guides Yuichi throughout the town, as his amnesia made him nearly forget everything in the town.
In her own route, Yuichi and Nayuki lived their daily lives until one day, Yuichi realized he was in love with her, and after some issues, the two reconciled after he confessed his feelings. Just when everything seemed fine, a car accident seriously wounded Akiko, Nayuki's mother, and put her under critical state. This event shocked Nayuki, as she began developing the fear of losing those who are dear to her. She constantly shunned Yuichi away each time he tried to comfort her. Dauntlessly, he continued with his effort to cheer Nayuki up.
In the end, Akiko finally recovered, and a happy Nayuki enjoys her newfound happiness with Yuichi.