Naoko was a classmate of Shoya, and in the same class that Shoko Nishimiya was transferred into. Although Shoya was not interested in girls in the sixth grade, nevertheless, Naoko always though of herself as his 'girlfriend'. She would look up to him, even though it was plain to everyone that he was a bully. When the bullying of Shoko began, Naoko joined right in, although what she did was mostly 'behind the scenes' to torment Shoko.
Later, as a senior in high school, she meets Shoko again. Naoko now works part time, as well as attending high school. However, she is a lonely, bitter, vengeful, and unloved teen. Her attitude towards Shoko is still the same, she dislikes her because Shoko supposedly 'stole' Shoya away from her. When the group of friends go to an amusement park, Naoko tags along. She invites Shoko to share a ride on the Ferris Wheel together. But when at the top of the ride, Naoko assaults Shoko verbally, as well as with an almighty slap to the face. At the hospital where Shoya is recovering from a fall from a third story balcony, Naoko again runs into Shoko, and not only berates her verbally, but physically assaults her and tries to impale her on a nearby chain link fence. She is stopped from doing so by an intervention by Shoko's mother.
Later, it appears that Naoko might be bisexual. She forms a loosely held shipping with Miyoko, and they live together in Tokyo while they both attend a fashion college on scholarships.