Yayoi has long black hair, red eyes and wears a kimono with a red bow on her head.
Long ago during the Taisho Era, she fell in love with an academic boy who was popular with girls, and wrote him many love letters. But he rejected her for a wealthy yet unattractive woman. And she came down with the flu while she was weak from the heartbreak, and passed away. However, her empty feeling of not truly being loved, since the boy kept her love letters in his collection of love letters from many different suitors, caused her spirit to linger. And as her feelings, which were infused into those letters, got condensed for having been contained in a box for years, she became an intense evil spirit of love.
Her spirit would be released when one of the boy’s descending family opened the box containing her love letters while cleaning the storehouse on their property. As she caused their son to be bedridden, they contacted Tsubasa to solve the problem, but although he drove her out, she would follow him in the hopes of experiencing a romantic relationship before passing on. Tsubasa agreed to fulfil her wish but as he experiences a lot of misfortunes, it became obvious that she hopes to take him to the afterlife with her. Yet Rinne warned her of the income, so she gave her thanks to Tsubasa and passed on.
- Yayoi is similar to Masahiro, who is also a ghost, from Urusei Yatsura. In both their stories, an exorcism is botched and the ghosts cling to the man who performed it, while the man is concerned about a living girl named Sakura getting jealous.