I'm watching Silence, I doubt it's perfect in its representation of the time period but it seems to present a picture in which missionaries more or less passively spread Christianity (as in, didn't force it like a conquering army) and it was subsequently harshly persecuted. Despite this many people remained fervently devoted to the religion and risked/gave their lives for it.
I'm curious what people would have found so appealing about it to convert in the first place, I can understand a devout believer withstanding torture and such, but it seems odd to me that people would entertain conversion let alone pay such high prices with no incentive other than spiritual fulfillment, especially when Shintoism and Buddhism were already well established.
I hope these previous posts of mine address to OP's curiosity:
Put it simply, not so small amount of the Japanese in the 16th century saw Christianity (Catholic brought by the Jesuit) as a kind of new, exotic Buddhist order at least in the beginning, thus did not understand it as a totally new 'religion'. The kind of 'syncretic', traditional Japanese religiosity, under the general moral code called 'Tendo' (divine providence), paved the way to this understanding, and they didn't generally attach somewhat significant meaning to the switching one 'religion' to another as the Christian Europeans did.
On the other hand, some Jesuit missionaries, under the auspice of Alessandro Valignano (d. 1606), were also willing to take 'adaptation' policies, that is to say, receptive to local circumstances and practices at least in the first phase, and established a school to educate local assistant clergy with the better understanding of such local practices.
These factors in Japan and among the Jesuit missionaries together probably contributed to the apparent success of the Jesuit mission in Japan, at least in its early years in the 16th century.