This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
Francis Xavier, a Jesuit missionary from the newly founded Society of Jesus, landed at Kagoshima in the Satsuma domain of Kyushu on 15 August 1549, opening the Society's mission to Japan. He remained in the country roughly two years before moving on to other mission fields in Asia, but the work he began did not end with his departure.
The mission Xavier founded grew rapidly under the Jesuits who followed him into Japan. What the standard literature calls Japan's Christian Century took its name from the scale that growth reached: at its height, the missions descended from Xavier's own initial landing had brought an estimated three hundred thousand Japanese converts into the faith, a substantial minority presence achieved within a matter of decades from a single missionary's brief stay.
That scale of conversion was not sustained. The same growth that made Christianity a visible presence across Kyushu and beyond eventually provoked one of the most systematic suppressions of Christianity carried out anywhere in its history, a reversal that unfolded over the decades following Xavier's own departure. What this changed for Christianity's spread was the opening, from one two year mission, of an entirely new field in East Asia: a convert population reaching several hundred thousand within a single Christian Century, planted by Xavier and sustained by the Jesuits who came after him, before the same government that had allowed it turned decisively against it.