|Played by||Shoma Yamamoto|
Seiji Hayami is a private detective operating at his Hayami Detective Agency and an ally of Honey Kisaragi in the battle against Panther Claw while writing a thesis about the evils of Japan's capitalism.
Seiji is a young man standing at average height with dark brown hair and eyes, wearing semi-formal clothing and is always seen with a tan colored flat hat.
Seiji is excitable and energetic about subjects that would do well in his thesis about the "demonish" things in modern Japan's capitalism. To fully understand this, Seiji began to live with Japan's homeless community and became a detective. He can get rather greedy in spite of his strong sense of justice and is easily swayed by a beautiful woman especially Yuki Kenmochi. His sense of justice however does allow him to choose ethics over success and common beliefs, this includes his genuine concern for Honey after she reveals her status as an android.
Seiji serves as an informant for Honey with various sources including the homeless community network that always seem to be on the right track. His other detective skills are not very good as he could only find rudimentary clues rather than all of them and usually has bad luck dealing with investigations like having to pay a large tab at a hostess club. While he is not very good at combat he possesses some equipment that helped out Honey when her Honey System went out of control. By the end of the series, he keeps a pistol to fight against Panther Claw combatants.
About 14 months prior to the series, Seiji got a notice at his detective office about from a girl named Mao who had her notebook stolen by a yakuza gang. Taking the case, proved to be more than Seiji could handle, partly because Mao was planning to use the folder to make money in a rival yakuza gang and had to run from the thugs. Encountering a fortune teller, the said fortune teller cast off her disguise to become Cutie Honey and fought off the gangsters. Ever since then, Seiji offered his services to Honey.
By recent times Seiji provides Honey information on Panther Claw and their operations while spending time with Gen-san and the homeless network. Often times he helps out Honey while getting himself in trouble with Panther Claw's schemes. Later encountering Miki Saotome and Yuki Kenmochi, he tries to court them but ends up failing (yet still tries). After Panther Claw's schemes get more severe, things start to get worse including when Yuki goes down a darker path in order to make Honey her property. While Seiji tries to keep the girls from killing each other off, he can only pass on messages given by Miki and Yuki after she has been fully corrupted.
At the end of the series, Yuki entrusts Honey to him and with Panther Claw under new management, Seiji decides to take his support of Honey more seriously. He Dr. Kisaragi's notes wanting to keep them from falling into the wrong hands and after reading them decides to burn it as it detailed Honey, Miki, and Yuki's origins as well as the working of their Honey Systems.