Hi - we as mods have approved this thread, because while this is a homework question, it is asking for clarification or resources, rather than the answer itself, which is fine according to our rules. This policy is further explained in this Rules Roundtable thread and this META Thread.

As a result, we'd also like to remind potential answerers to follow our rules on homework - please make sure that your answers focus appropriately on clarifications and detailing the resources that OP could be using.

Additionally, while users may be able to help you out with specifics relating to your question, we also have plenty of information on /r/AskHistorians on how to find and understand good sources in general. For instance, please check out our six-part series, "Finding and Understanding Sources", which has a wealth of information that may be useful for finding and understanding information for your essay.

Although the AH reading list ought always to be a first port of call, the books on it that deal with Japan in this period aren't really focused on foreign relations, and a lot of what has been written on Japan's encounter with the world focuses on the Tokugawa period, so I'll suggest some more specialist titles to you. Unfortunately I'm not familiar with French-language historiography in this field, but among books in English I'd suggest checking out the following.

The classical starting point is C.R. Boxer's The Christian Century in Japan, which first appeared way back in 1951 but was updated in fresh editions into the 1990s – try to get hold of the latter. It remains a title to be aware of, even though it's pretty hefty and adopts a partially narrative approach; a lot of what has been written since is a response to it and its ideas. A rather more modern counterpoise that makes a good starting point is Jurgis Ellisonas's chapter "Christianity and the daimyo" in The Cambridge History of Japan: Early modern Japan (1991), pp 301–371.

The main Christian countries that Japan was in contact with in this period were Portugal and Spain. I've found the following helpful in the past:

• Thomas Baker, "Pulling the Spanish out of the 'Christian century': re-evaluating Spanish-Japanese relations during the seventeenth century." Eras, 2009. This was available online the last time I needed it, but the link that I kept doesn't work now – worth searching digitally for it, though, I'd think. Again, despite its title, it does touch on events in the C16th.

Boxer, again, has two more works – note he was an historian of Portugal more than he was an historian of Japan, so the former in particular will be rewarding:

• Portuguese Merchants and Missionaries in Feudal Japan, 1543-1640 (1986)
•  "When the twain first met: European conceptions of Japan, sixteenth to eighteenth centuries." Modern Asian Studies, 1984

Although the history of the Japanese and Dutch really becomes important in the C17th-18th., it did just about start in your period. There's a recent study that focuses in depth on the whole relationship, and which does touch on what happened in the Sengoku era:

• Adam Clulow, The Company and the Shogun: the Dutch Encounter with Tokugawa Japan (2014)

Beyond that, I would recommend trying to get hold of a couple of case studies looking at opposite ends of the contact spectrum: Tomoko Kitagawa's "The conversion of Hideyoshi's daughter Gō" in Japanese Journal of Religious Studies 34 (2007) and Michael Cooper's The Japanese Mission to Europe, 1582–1590; The journey of Four Samurai Boys through Portugal, Spain and Italy (2005).

I hope this helps!