[Answer]
Japan extends
its nationality either by virtue of “birth,” by “notification,” or by way of
“naturalization.”
A person
acquires Japanese nationality by birth;
1) When either parent is a Japanese national at the time of birth (A child
born to a Japanese mother is automatically granted Japanese nationality,
regardless of the nationality of the father and whether they are married,
but a child born out of wedlock to a foreign mother and a Japanese father
is granted Japanese nationality only when the father recognizes the child
as his while the baby is still in the mother’s womb.)
(1)
When the father dies before the birth and is a Japanese
national at the time of death
(2)
When a person was born on Japanese soil and both parents
are unknown or stateless
A person acquires
Japanese nationality by “notification”;
(1)
When an underage person whose father or mother has
acknowledged paternity or maternity respectively, if the father or mother is a
Japanese national at the time of the person’s birth, and such father or mother
who made the acknowledgement is presently a Japanese national. According to the
Article 3 of the Nationality Law, a person who made the notification shall
acquire Japanese nationality at the time of the notification. The law was
revised on January 1, 2009 following the Supreme Court ruling that denying
Japanese nationality to children born out of wedlock to foreign mothers is
unconstitutional. Such notification can be made with the Legal Affairs Bureau
if the person lives in Japan and with the foreign establishments if the person
lives abroad.
(2)
When
a person who had lost Japanese nationality retroactively from the time of birth
due to failure to notify the authorities within three months of the birth of
the intention to retain Japanese nationality, and apply to reacquire
nationality if the person is under 20 years old and lives in Japan.
A person acquires Japanese nationality by “naturalization," please refer to the following item on naturalization.