Appears in the story "The Case of Yoshiko and Haruko". Haruko is Yoshiko's friend and hopes to obtain Tanaka's love by hunting down a mermaid. She becomes more invested in the hunt than Yoshiko, and eventually confesses to knowing more about the myth of the mermaid's flesh than she initially let on. In [i]The Case of Mariko and Kaori", it is revealed that Haruko is friends with Kaori and tells her about the mermaid's flesh myth. In the first volume's end notes, it is stated that her earlier name was "Nobuko". In chapter 8, Misaki mentions that "Nobuko of class 1" is dating Tanaka.