Age of consent is one of those things that varies by location (edit: and sometimes circumstance now that I think about it, such as someone being married very young with parental consent), so whatever our thoughts on the matter her partner may not have done anything illegal at any rate
It would still be illegal since the mother was 14 .
In Japan ,the age of consent was put to 13 in 1907 (Penal Code) ,after WW2 ,Japanese prefecture (City and District within prefecture too) could pass an ordinance and it would put the age of consent at 18 instead in the area ,here when they did it (Prefecture only) :
Okayama :1950 (1/47)
Wakayama :1951 (2/47)
Kagawa :10th of August 1952 (3/47)
Kanagawa :4th January 1955 (4/47)
Hokkaido :2nd of April 1955 (5/47)
Fukuoka :1956 (6/47)
Osaka :1956 (7/47)
Nagasaki :1957 (8/47)
Yamaguchi :13th of December 1957 (9/47)
Hyogo :1958 (10/47)
Kochi :1958 (11/47)
Ishikawa :1959 (12/47)
Miyagi :31th of March 1960 (13/47)
Gifu :10th of November 1960 (14/47)
Aichi :28th of March 1961 (15/47)
Gunma :1st of April 1961 (16/47)
Shizuoka :4th of October 1961 (17/47)
Kagoshima :22th of December 1961 (18/47)
Ibaraki :6th of October 1962 (19/47)
Fukui :1st of April 1964 (20/47)
Yamanashi :2nd of April 1964 (21/47)
Tokyo :1st of August 1964 (22/47)
Chiba :1st of November 1964 (23/47)
Shimane :26th of March 1965 (24/47)
Tokushima :19th of July 1965 (25/47)
Oita :15th of April 1966 (26/47)
Ehime :6th of October 1967 (27/47)
Kumamoto :8th of June 1971 (28/47)
Mie :24th of December 1971 (29/47)
Okinawa :15th of May 1972 (On the exact same day the USA gave back Okinawa to Japan) (30/47)
Tochigi :6th of July 1976 (31/47)
Nara :22th of December 1976 (32/47)
Toyama :25th of March 1977 (33/47)
Niigata :31th of March 1977 (34/47)
Miyazaki :28th of July 1977 (35/47)
Saga :29th of July 1977 (36/47)
Shiga :23th of December 1977 (37/47)
Fukushima :30th of March 1978 (38/47)
Akita :5th of October 1978 (39/47)
Hiroshima :13th of March 1979 (40/47)
Yamagata :26th of March 1979 (41/47)
Iwate :21th of December 1979 (42/47)
Aomori :24th of December 1979 (43/47)
Tottori :25th of December 1980 (44/47)
Kyoto :9th of January 1981 (45/47)
Saitama :1st of November 1983 (46/47)
Nagano :1st of July 2016 (47/47)
The reason Nagano prefecture did it so late is because subdivisions in the prefecture (City and District) already passed the ordinance themselves ,so the prefecture itself didn't feel the need to do it .
And Japan put the age of consent at 16 in 2023 ,you could say it's useless since it's already 18 in all the prefecture ,but it's just in case ,because they could just repel the ordinance if they wanted .
So 14 prefecture out of 47 in the 50s ,13 in the 60s (27/47) ,17 in the 70s (44/47) ,2 in the 80s (46/47) and 1 in the 2010s (47/47)