Eisuke is Ran's new classmate. The two met shortly following the 'Black Impact' incident in which the FBI apprehended a member of the Black Organization via a fluke accident, about which Eisuke appears very curious.
His deductive skills are not very impressive, though Detective Moore has offered Eisuke the opportunity to visit his agency at any time. Eisuke seems to have impeccable timing throughout his short time in the series, and he is very accident prone. He also has a crush on Ran.
Conan originally suspects Eisuke of being involved with the Black Organization; however, it is unclear as to who he works for or if he is actually a member of the Black Organization at all. For instance, in one case, Eisuke broke down in tears because he was "unable to solve the mystery." However, suspicions regarding Eisuke's true identity for Case Closed enthusiasts increases as Gin recalls hearing someone say "Hondou... Hondou... Hondou..." before.
Conan also notices many similarities between Eisuke and Rena Mizunashi, and this leads Conan to believe that the two are related. However, viewers may infer that the Black Organization's relation with Eisuke goes deeper. In File 604, it is revealed that "Rena" is actually Eisuke's sister Hidemi, who is an undercover CIA agent like their deceased father, Ethan. After Mizunashi returns to the Black Organization, the FBI tries to get Eisuke to enter the witness protection program. However, Eisuke returns in File 619, and has refused to be protected by the FBI.
Surprisingly in File 621, Eisuke tricks Conan into revealing his secret identity to him by telling Conan that he is in love with Ran and that he wants to travel to America to become a CIA agent and take her with him. However, he muses that he wanted to talk to Shinichi to get his opinion, since he knows the two had sort of been together and is angry that Shinichi is not there more for her. Conan then firmly reveals his opinion on the matter as well as who he is. Eisuke only laughs and tells Conan he had suspected it all along. Before leaving, Eisuke asks Conan to make Ran happy.