Junko is a student of class 1-A and the class representative. She is a disciple of the god Suhara and a member of the Iga Ninja Clan. Her family of warriors have been charged with protecting the Empire for generations. She is very devoted to her samurai-like traditions and has a strong sense of justice. She meets Akuto on the train to the school, and forms a pact with him to make the world a better place. When she discovers that he is destined to become Demon King, she decides that it is in the best interest of society to destroy him, believing that he knew about his destiny and that he tricked her into becoming friends. She usually misinterprets his attempts at good deeds and intentions as evil wrongdoings.
She begins to develop strong feelings for Akuto throughout the series after realizing his intentions, and at one point didn't mind the thought of being married to him. According to Kena Soga, Junko is Akuto's best friend, and according to Korone, Junko and Akuto should get married. Her goal is to serve the nation as a member of its fighting force. In the anime and to some extent in the manga, she is portrayed as having tsundere tendencies.
Her power is mostly based around the sword that she carries with her at all times.
- Her family name is taken from the famous samurai Hattori Hanzō.