Contrary to conspiracy theories circulating in some parts of this website, I am not secretly an official within the Japanese government, nor the child of any such official, nor a contractor hired on their behalf, my darling Anon.  (I consider myself an American.  This nation’s fate is my fate.)

So let’s go farm Wikipedia:

In 1873, following the Meiji Restoration, the ban was rescinded, freedom of religion was promulgated, and Protestant missionaries (プロテスタント Purotesutanto or 新教 Shinkyō, “renewed teaching”) began to proselytise in Japan, intensifying their activities after World War II, yet they were never as successful as in Korea.

Today, there are 1 to 3 million Christians in Japan, most of them living in the western part of the country, where the missionaries’ activities were greatest during the 16th century. Nagasaki Prefecture has the highest percentage of Christians: about 5.1% in 1996.[39] As of 2007 there are 32,036 Christian priests and pastors in Japan.[26] Throughout the latest century, some Western customs originally related to Christianity (including Western style weddings, Valentine’s Day and Christmas) have become popular among many Japanese.

About 2.3% of Japan identifies as Christian.

A number of Asian-Americans within America are Christian, but that does not necessarily apply to the ancestral countries.

Korea, on the other hand, is far more Christian for some reason.

According to the national census conducted in 2015, 19.7% of the population belongs to Protestantism, 15.5% to Buddhism (Korean Buddhism), and 7.9% to the Roman Catholic Church; in total Christianity is the religion of 27.6% of the Korean population.

I can’t pretend to see inside the minds of the ruling Liberal Democratic Party, but apparently, while it is showing signs of strain, the LDP is in a coalition with another party closely aligned with a Buddhist religious movement…

So I’m going to guess that no, they won’t push Catholicism to try to increase birthrates, that it isn’t really part of the vision of Japanese national identity the ruling classes in Japan have.

But someone currently living in Japan would be better to ask.

With that said, given the outcomes for Protestant countries vs Catholic countries, that certainly isn’t a tradeoff I’d make until after I’d exhausted other options, like getting Japanese people to spend less time at work so they can actually meet members of the opposite sex and form families.