about Shirou and 'kirishitan' ( Old Japanese Christian.)

Christianity was intoroduced by Francisco de Xavier (or Francisvo de Gassu y Javier) in 1549 in Japan. Buddhism ( or Shinto ) was believed in at the time in Japan but people who was converted to Christianity grew and grew from then.
An old Japanese government decided to put a ban on Christianity because it could be a serious threat to the goverment's power. So Japanese christians had to pray images of buddism saints ( Miroku-bosatsu and Kannon-zou * ) instead of images of Jesus Christ and the Virgin Mary to escape from watch of the government.
( * That Kannon-zou is now called ' Mary Kannon ' in Japan.)
And Shirou rose up against the government with the people, but all of them were killed in the end. He was only 17 years old at the time. That's a sad history.
Of cource there's freedom of religion in modern Japan and most present-days Japanese have no particular religion. ( We enjoy Christmas Day and spend New Year's Eve hearing Buddhism Temples' bells ringing and visit Shinto shrines to celebrate Happy New Year. )

By the way, old Japanese christians' costumes influenced people called ' Kabuki-mono ', that meant like punk rockers or something. The kabuki-mono liked colorful clothings, and took the western clothings and crosses in their fashion.
And the KABUKI, the traditional stages, was actually from this Kabuki-mono. A woman called Okuni created a new performance wearing Kabuki-mono's clothings and putting a cross on, and the performance became being called KABUKI.
( However, Woman's KABUKI was put a ban on by an old Japanese government a few years later. There's no woman actor in the KABUKI world from then, although a woman created it.)

So the KABUKI was never born without western culture. I think that's interesting.

Edit:
He's very famous in Japan、and there're a lot of a lot of stories/mangas/novels/movies about him.
If you know some manga about him, it's just one of them.
Almost every "Shirou" looks like this, because he originally looked like this.
I just drew the original Shirou with a little of my tastes.
Sorry if I don't know the shirous in mangas you've read.