Japan adopts the principle of jus sanguinis (right of blood). Nevertheless, even among children born to a Japanese father or mother, there are many who do not possess Japanese nationality from birth.
Conversely, there are also cases where a child born to two Japanese parents holds double/multiple nationalities at birth.
Why does such a difference arise?
A major factor is whether the parent(s) submitted the birth notification to a Japanese administrative authority within the statutory filing period.
Suppose a child is born abroad to a Japanese parent and a non-Japanese spouse and acquires a foreign nationality at birth. Because Japan is a country that does not recognize dual nationality in principle, one might assume that such a child cannot acquire Japanese nationality once a foreign nationality is obtained.
However, a newborn obviously cannot choose between Japanese and foreign nationality at the moment of birth. Therefore, as a special grace measure, if the parent(s) submit a birth notification within the statutory period (within three months for a child born abroad) and simultaneously declare their intention to reserve Japanese nationality, the child is allowed to hold double/multiple nationalities.
On the other hand, if a child is born abroad, acquires a foreign nationality, and the Japanese parent fails to submit the birth notification within the required period, then as a general rule, no remedial measures are available after the deadline.
While certain remedial options may exist if the child comes to Japan as a minor, registers residency, and resides in Japan for some time…that will be explained on another occasion.
Once the child becomes an adult, all recovery options disappear.
Therefore, if the parents wish their child to maintain dual or multiple nationalities, it is essential to submit the birth notification with the declaration to reserve Japanese nationality immediately after birth.
If no birth notification is filed and the child reaches adulthood, it becomes impossible for the child to obtain or maintain dual/multiple nationality, meaning Japanese nationality in combination with any foreign nationality. As a result, many such individuals end up possessing only the foreign nationality.
Meanwhile, there are also cases in which a child born to two Japanese parents acquires three nationalities at birth.
In one such case, a Japanese man was born in Country A, which follows jus soli (right of soil). Therefore, at birth he automatically acquired both Japanese nationality and nationality A.
He later married a Japanese woman and they had a child who was born in Country B.
Because their child was born in Country B—another jus soli country—the child acquired at birth nationality A, nationality B, and Japanese nationality.
(This was possible because the parents properly filed the birth notification with the Japanese nationality-reservation declaration within the statutory period.)
Under Japan’s Nationality Act, dual/multiple nationals are required to choose a nationality by the age of 20.
If they fail to choose by the deadline, the Minister of Justice may issue a demand for nationality selection. If the individual does not choose Japanese nationality within one month after receiving such a demand, they may lose Japanese nationality.
However, according to information obtained from Diet deliberations, there has been no case to date in which a dual/multiple national at birth has been issued this demand.
(That said, future administrative practice may change; this statement reflects the situation as of November 2025.)
Additionally, if a minor voluntarily acquires a foreign nationality—
for example, a minor born in Japan to Japanese parents who originally possessed only Japanese nationality—
the child loses Japanese nationality at the moment the foreign nationality is acquired.
This point requires careful attention.