At first, their relationship is somewhat unclear, with Sunako initially saying that she wants to kill Kyohei, and even going to the extent of turning into a lady temporarily to get him back. Her reason is that "she's the only person who can kill him". She has not, however, thought of or mentioned killing Kyohei for many chapters, not even after Kyohei kissed her. Recent chapters have seen her forget her first crush, and she is now more open to other people, including her peers and teachers at school. She's also having less and less nosebleeds and though protests at first, doesn't greatly mind spending time with Kyohei. In the manga, Sunako and Kyohei's relationship begins to head in a romantic direction, although they are both completely inexperienced with those feelings and don't realize their connection.
Sunako has a growing fascination with Kyohei, as he is the one boy who most closely resembles her in personality. Despite the observations of passers-by, both parties claim that there is no attraction to each other. However, as the series progresses, both begin to see each other in different lights as previous assumptions are proven wrong. Though she does not seek a relationship, her relationship with Kyohei grows to where they seem fond of the other though they may not know it.
In Volume 18, Kyohei surprises Sunako with a kiss. Although Kyohei claimed the kiss was an act of confusion, Sunako realizes that she doesn't hate Kyohei anymore, and doesn't find him as radiant anymore, which proves that she begins to see Kyohei in a different light and starts to gradually know her attraction for him.
In Chapter 126, there's a new character named Yuki-chan who casts a spell on Kyohei, believing that Kyohei and Sunako are in love but Kyohei doesn't show his love for Sunako. Yuki-chan's spell makes Kyohei cold as ice, and the only way to end her curse is for him to have intercourse with the woman he loves. Though the two are a bit hesitant at first, especially Sunako, she comes to agree to be alone in a room with Kyohei when he says that Sunako is his "precious friend." The two stare longingly at each other for a while, then Kyohei breaks the spell Yuki-chan cast on him without having intercourse.