The Diplomat Kosaku Kuroda - Season 1

A terrorist threatens to disrupt a World Conference.

Kosaku Kuroda (Yuji Oda) returns to Japan after 11 years to investigate the death of Tsuyoshi Shimomura (Teruyuki Kagawa), a murder suspect who committed suicide in San Francisco. Kuroda's swift return was arranged by his superior, Yosuke Ando (Takeshi Kaga), the head of the Japanese Citizen Anti-Terrorism Office. However, the move is also influenced by Vice Minister of Foreign Affairs, Shoko Kanjo (Tamiyo Kusakari), who wants to closely observe their actions.

Kosaku Kuroda (Yuji Oda) grows more certain that Tsuyoshi Shimomura (Teruyuki Kagawa) is still alive after Rikako Ogaki (Ko Shibasaki) claims to have seen him at a party. Kuroda asks Vice Minister of Foreign Affairs Shoko Kanjo (Tamiyo Kusakari) to use her authority to open an investigation, but she refuses, stating that Rikako's testimony alone isn't enough to act on.

While investigating the whereabouts of Tsuyoshi Shimomura (Teruyuki Kagawa), Kosaku Kuroda (Yuji Oda) finds himself in the middle of another murder. Someone kills Tsutomu Kashiwada (Ren Yagami), who had been threatening Rui Shimomura's (Kaho) friend, Yutaro Kimijima (Takahiro Nishijima). Kuroda and Rikako Ogaki (Ko Shibasaki), who were at the scene after the murder, become increasingly scrutinized by their respective departments.

Kosaku Kuroda (Yuji Oda) helps Princess Sara (Jenya) of Alitoria escape. Kuroda respects Sara's decision to refuse to sign the memorandum for a power plant construction project that was pushed by both Japan and Alitoria, as he became aware of its shoddy nature and her desire to protect her country's nature. However, the situation turns into a disappearance case involving the police. Cornered by the police, Kuroda enlists Rikako Ogaki (Ko Shibasaki) to help him break through the cordon.

From a conversation with Aiko Sasaki (Nana Katase), Kosaku Kuroda (Yuji Oda) learns that a series of incidents involving Tsuyoshi Shimomura (Teruyuki Kagawa) may have been caused by a drug-induced litigation case. To confirm the truth, Kuroda visits Susumu Yoshimura (Hiroshi Okochi), the president of Brighton Japan Pharmaceuticals, who was a defendant in the case, at a new product launch.

Behind a series of murders involving Tsuyoshi Shimomura (Teruyuki Kagawa) that Kosaku Kuroda (Yuji Oda) is investigating, is a lawsuit over a drug called Atron, which was produced by Brighton Pharmaceuticals, an American-based company. The son of Takashige Yamaji (Ryo Iwamatsu), who attacked Rikako Ogaki (Ko Shibasaki) as she got closer to the truth, also died from the side effects of Atron.

Kosaku Kuroda (Yuji Oda) and Rikako Ogaki (Ko Shibasaki) track down Tsuyoshi Shimomura's (Teruyuki Kagawa) hideout, but he gets away due to Rui's (Kaho) interference. Afterwards, Rui disappears with Yutaro Kimijima (Takahiro Nishijima).

Kosaku Kuroda (Yuji Oda) asks Foreign Minister Shusuke Saito (Masaomi Kondo) for permission to negotiate with Tsuyoshi Shimomura (Teruyuki Kagawa), who has taken former Prime Minister Seiichiro Yatabe (Sei Hiraizumi) hostage in a waiting room at a diplomatic conference venue.

Kosaku Kuroda (Yuji Oda)'s investigation appears to be concluding with the deaths of Tsuyoshi Shimomura (Teruyuki Kagawa) and Keiichi Yuki (Masato Hagiwara), and the arrest of Aiko Sasaki (Nana Katase). The government seals off the information that the standoff by Shimomura and his group was an act of terrorism motivated by anger over the Atron drug.