Some reports have identified him as 34-year-old Yuki Imai, who has lived in Russia since at least 2014 and studied at Saint Petersburg State University; he has reported on Russia-North Korea relations and on North Korean nationals living in Sakhalin. Those same reports say the FSB's allegation centers on military personnel sent from the Kuril Islands to fight in Ukraine. Other accounts describe the suspected espionage only in general terms, without naming the journalist or specifying that detail. If convicted, he faces a sentence of 10 to 20 years.

The arrest comes four days after Japan lodged a formal protest against Russia's demand for the extradition of Tomoko Akane, president of the International Criminal Court. It also follows weeks of deteriorating relations between Moscow and Tokyo after President Vladimir Putin visited Iturup, one of the islands in a chain Russia calls the Kuril Islands and Japan calls the Northern Territories, in August. Japanese Prime Minister Sanae Takaichi called the visit "incompatible with the Japanese position" and "absolutely unacceptable," saying it dealt a blow to relations already strained by the war in Ukraine. Moscow summoned Japan's ambassador in response, protesting what it called Takaichi's "anti-Russia" statements, and has said Russia's sovereignty over the southern Kuril Islands is "absolutely unshakable."

Russia classifies Japan as an "unfriendly" country over Tokyo's participation in Western sanctions tied to the war in Ukraine. Japan's embassy in Moscow did not respond to calls placed outside business hours, and Tokyo has said it will keep its sanctions and support for Ukraine in place.

The territorial dispute over the islands has blocked a formal peace treaty between Russia and Japan since the end of World War II, despite decades of diplomatic efforts. Russia has a record of arresting foreign nationals on espionage-related charges; Wall Street Journal reporter Evan Gershkovich was detained in 2023, sentenced to 16 years, and released the following August in an East-West prisoner swap that also freed journalist Alsu Kurmasheva.