It seems the current government has introduced legislation to alter the Imperial House laws.

Male line descendants of junior Imperial lines that were removed in 1947 can be adopted back into the family in order to become members of the Imperial family and be eligible for succession after the current heirs (crown prince, his son and the emperor's uncle).

The second alteration allows Imperial princesses to keep their style, title and membership of the Imperial House after marrying a commoner. Their spouse and offspring however do not become part of the Imperial family.

Both alterations solve the problems facing the Imperial family.
1 having heirs who for fill the required male line descendence of the first Emperor
2 retaining male succession as the emperor also has a religious function within the Shinto religion and has to perform certain rituals.
3 retaining enough working royals to provide the reigning emperor and his successors enough support of relatives in representational roles. That is something, the currently unwed princesses can do after their marriages if they choose to do it.


What many seem to forget in this discussion the the religious role of the Emperor. Yes Empresses have reigned before but their successor was always another male line descendant of the first emperor.
It also prevents a break in those religious rituals that can only be performed by the male emperor.

I always compare it to the Roman Catholic Church and the Vatican state. Most people understand that it's not so easy to elect a female pope any time soon. The same applies for Japan. The Emperor is not a purely secular role and as such religious arguments and requirements have to be taken into account.