How do Catholics in Japan celebrate the Feast of the Discovery of the Hidden Christians? Most people know that March 17 is the Feast of St Patrick. But in Japan, the faithful celebrate the Feast of the Discovery of the Hidden Christians or Kakure Krishistans.

In 1614, all Catholic missionaries were expelled from Japanese soil. Fr. B. Petitjean arrived in Nagasaki, Japan in August 1864 and was able to construct a small Church. On March 17, 1865 he discovered that the Christian faith had survived in Japan for some 250 years without any missionaries (priests) to administer the sacraments!

Outside the celebration of the Mass for this feast, how do Japanese Catholics celebrate this feast?
We attend the Holy Sacrifice of the Altar, i.e. we "have Mass". I recall two or three years ago the priest gave a homily about it at Mass one night; apparently it was a Tuesday night.

It's not a big deal in my city, at least (which, with a population of more than 300,000, has only one Sunday sacrifice (in a church smaller than most American churches), that's how few Christians of the catholic faith there are).

"Having Mass" to celebrate perhaps shouldn't surprise you, since it is "the source and summit of our faith", the highest celebration, etc. 

The Christians in Japan really need your prayers, by the way. The catechesis, evangelization, birth rate, and seminarians all appear to be really struggling, and there is still nationalism among the Japanese such that multiple times I have been told, "Of course I'm not Christian, because I am Japanese."