Akira Hino and Taeko Nagafuji are recurring characters in the Adachi & Shimamura light novel series who often serve as foils for series protagonists Sakura Adachi and Hougetsu Shimamura. While both characters are featured in the anime and manga adaptations, they are not afforded the same level of depth and development compared to the source material.
In Adachi & Shimamura Vol. 2, both Hino and Nagafuji get interlude chapters told from their perspectives, which helps flesh out their characters. Not only do readers get to learn more about who they are as individuals independent of their relationships with the protagonists, but some of their personality traits start to make more sense in greater context as well. Between the two, Nagafuji gets the most development and is the character most of the others have trouble understanding.
When examining Nagafuji's personality and behavioral traits in the second light novel, certain patterns start to emerge that seem to point to her having high-functioning autism. One of the first major clues to this is the fact Nagafuji is book-smart but struggles significantly with social situations. This is noted by both Hino and Shimamura in particular. While both girls admire and respect Nagafuji for her intelligence and high academic performance, they also struggle to communicate with her effectively, which is a major source of frustration for them both.
Throughout the second light novel, Nagafuji is constantly depicted as existing in her own little world, and tends to interpret situations and people's intentions very differently. This is commented on by both Hino and Shimamura at different points in the book, with Hino adding that Nagafuji tends to learn at a different pace from others. They especially take note of the fact that jokes and nuance are easily lost on Nagafuji, finding themselves having to explain what they really mean to her. Ironically, Nagafuji's own sense of humor is also easily lost on both Hino and Shimamura, largely because she tends to say exactly what's on her mind, with both girls trying to decode her meaning by overanalyzing her words.
Related to that last point, Nagafuji struggles to read social cues and is not able to tell when her friends are annoyed with her behavior. This is most evident when Shimamura invites Nagafuji to go Christmas shopping with her at a local mall, only for Shimamura to find the whole endeavor frustrating. Originally, Shimamura solicited Nagafuji's help in picking out a Christmas present for her "little sister" (in reality, the gift was for Adachi), but quickly learned how easily distracted she got by things that caught her interest. While it was obvious to an outside observer that Shimamura was growing impatient with Nagafuji's inability to stay on task, Nagafuji herself didn't sense a problem.
Another aspect of Nagafuji's personality that hints at her having high-functioning autism is that she has very fixed interests as well as inflexible routines. This is also largely noted in the Christmas chapters of the second volume. In the chapter where she shops with Shimamura, despite knowing she's there to help the latter pick out a present for her "sister," Nagafuji ends up guiding Shimamura based on her own personal interests. Since Nagafuji is a huge food lover, she tries several times to get Shimamura to buy food as a Christmas present for her "sister," with Shimamura declining each and every time. She eventually ends up talking Shimamura into getting a boomerang for Adachi after buying one for herself.
In her interlude chapters with Hino, the latter notes that Nagafuji's family has chicken curry every Christmas, which is different from the Japanese tradition of eating fried chicken on the holiday. When asked why her family has chicken curry every year, Nagafuji answers that that's what she tells her parents to make every year when they have her decide their holiday meal. Nagafuji even tends to mark Dec. 25 as her curry day on the calendar.
Another way Nagafuji demonstrates inflexible interests is when she's tasked with coming up with a new mascot for her family's butcher shop. She shows a profound lack of interest in this task by drawing whatever comes to her mind -- in this case, a parakeet. Hino finds the choice of a parakeet to be strange and decides to help her with the task.
While Hino is sometimes frustrated by Nagafuji's limited interests and social challenges, she also shows that she cares for her to the point where it doesn't negatively impact their friendship. Even when Hino tries to have a serious conversation with her about their future once they grow up and start living as adults, Nagafuji doesn't believe they'll stop being friends. While Hino thinks this is unrealistic at first, she ultimately accepts the fact that Nagafuji will always want to be a part of her life.
