The Tokyo District Court ruled on Thursday that Japan's dual nationality ban was constitutional, rejecting a claim by a teenage plaintiff who had lost his Japanese citizenship after acquiring British citizenship.

The 14-year-old plaintiff sued the state in 2023, saying his parents' decision to acquire British citizenship for him was invalid, citing Article 11 of the nationality law, which states individuals will lose their Japanese nationality when they acquire a foreign nationality “at their own choice.”

He also argued that the nationality law, itself, violates the Constitution if applied to a minor such as himself. In Japan, dual-nationals are asked to choose one nationality or the other before they reach the age of 22.

Born in 2010 to Japanese parents, the plaintiff was born as a Japanese national. He was later adopted by a couple — a Japanese woman and a British man — and registered for British citizenship.

During the COVID-19 pandemic, the plaintiff’s Japanese passport expired. When he tried to renew his passport at the Japanese Embassy in the U.K., he was told that he had lost his Japanese nationality based on Article 11 of the nationality law.

The lawsuit centered on whether the parents' decision to acquire British citizenship for the child could be regarded as a decision made by the plaintiff.

Presiding Judge Yukio Shinada said that the parents’ decision to acquire U.K. citizenship is valid because, as legal representatives, they can make decisions on behalf of the child, who is a minor.

The plaintiff’s legal team called the ruling unfair as the judge failed to take the plaintiff’s situation into account.

“If one is not aware of the law, they may not understand that acquiring foreign nationality results in the loss of Japanese nationality. Most Japanese are not aware of this,” said Teruo Naka, a lawyer representing the plaintiff.

“The existence of this law and the supposed opportunity to choose (one’s nationality) is merely on paper. It raises the question of whether it is acceptable for someone to lose something as important as nationality based on such a stance.”

Last week, the Fukuoka High Court dismissed a similar case in which the plaintiff sued the government for not allowing dual nationalities.