Answer:
Japan.
Step-by-step explanation:
The area that I think last became Christian was Japan. I think it was the last to become Christian due to a variety of factors, including an isolated geography, the lack of a direct trade route with the Middle East and Europe, and the Japanese people's unique cultural and religious beliefs. Additionally, Christianity was actively suppressed by the Tokugawa government during the Edo period, which made it difficult for the religion to flourish in the country. It wasn't until the 19th century that Christianity was officially recognized as a religion, but by then it was already marginalized as the dominant religions in Japan, such as Shintoism and Buddhism, had already taken root.