Since her older sister Yumi refuses point-blank to run the Ryokan Hiei like tradition dictates she should, Miwako runs the inn in her stead. Although Miwako enjoys running the ryokan and would gladly take over as manager, her grandmother, Takae, is nettled at this disregard for tradition and never mentions all the work Miwako puts into the ryokan, something she is rather bitter about. This tricky situation causes Miwako to resent Yumi both for being the oldest and for not helping.
In 2010, Nancy Drew has a reservation at the Ryokan Hiei as a reward for helping P.G. Krolmeister in Trail of the Twister. However, Nancy soon becomes aware of the ryokan's reputation for being haunted, and even experiences some ghostly encounters herself. Whenever she mentions these encounters to Miwako though, the young manager appears to be emotionally fragile and insists that Nancy must be imagining things. Nancy finds it very difficult to talk to Miwako, who absolutely refuses to talk about both her mother's mysterious death and anything to do with the ryokan's hauntings. She may even throw Nancy out of the game if she gets too nosy.
Though usually appearing calm and quiet, she nevertheless seems very frightened and tense under the surface, and also harbors a lot of anger towards her sister for being "bratty and manipulative"; her grandmother for not appreciating all the work she does and the insistence that unhelpful Yumi should run the inn; and her boyfriend Rentaro for always trying to convince her to move to the city with him. She is also angry at herself for not being with her mother when she died, believing that since everyone was at the ryokan at the time, someone should have been able to help her.
Nancy eventually finds a letter from Kasumi in the hidden baths, saying that she wants her daughters to stop fighting and work together, telling them that it's okay if neither of them wants to manage the ryokan and simply wants them each to live their lives the way they want. Miwako, who has always enjoyed running Ryokan Hiei, happily becomes its manager and Yumi, now that she no longer feels pressure to run the place, visits the ryokan more often and even begins catering her bento there. Without that source of friction, the sisters are able to stop fighting so much and become closer.
Nancy also discovers that Rentaro was the one scaring away the ryokan's clients by faking all the hauntings. He had hoped to force his stubborn girlfriend to leave the ryokan and move to the city with him because he believed the ryokan held to much pain for her to be truly happy. Depending on whether Nancy chooses to turn Rentaro in or allow him to confess to Miwako himself, he either leaves and is never seen again or apologizes for many months until a furious Miwako permits him to work at the ryokan again, undoing the damage he inflicted. Although she understandably broke up with him, he hopes that she'll eventually come around. Nancy thinks that's unlikely.
- Miwako absolutely adores her pet robotic cat, Suki. She's not allowed to have a real pet cat at the ryokan, so she was elated when Rentaro gave Suki to her as a gift.
- Miwako is surprisingly tall.
- Inspired by Suki, Rentaro planned on giving Miwako a robotic dog that he was working on.
- Miwako was only thirteen when Kasumi died.
- Miwako and Rentaro have been dating for four years and seven months.
- "You work too hard, Nancy-san. Up too late, off to teach so early. You must rest more. Your judgment suffers if you do not get enough rest."
- "Every day I'm here, making sure all is well- it would just be nice to hear [Takae] at least mention all the work I do. Just once."
- "With [Yumi and me], the term isn't 'close', it's 'within striking range'. So we both try to avoid that."
- "Help? You want to help? Look around you. This place is beyond help. It was spooky and lonely before... everything that happened happened, and now... Why do you think Yumi go out of this place as soon as she could? People come because they've heard it's haunted, they come here to be scared, and even they can't take it."