Bear in mind that Japan is a non-Christian nation, with Christians forming only about 1% of the population, plus, the non-Christians there have had a long history appropriating imagery from other religions because it looks nice. The Jesuits missionaries from Portugal and Spain wrote back to their superiors about people carrying/wearing rosaries and crucifixes even though they weren’t Christian or even interested in learning about Christianity or becoming Christian. Think about the odd use of Christian imagery and concepts from Kabbalah which all over the place in “Neon Genesis Evangelion” one of the creators of which admitted that they used it because it “looked good”. Or the wonky but lovingly portrayed version of the Catholic Church in “Trinity Blood”: there really *was* a fourteen year old Pope back in the 400s or somesuch, but I doubt the Church is going to give Holy Orders to androids, or elect nuns to serve as bishops, though in a post-apocalyptic world, a brave nun very well might step in to do as much as she can to keep the Christians together and help keep simple religious ceremonies going, which actually happened in Japan in the 1600s, when the Tokugawa regime forced all the Europeans out of the country, including dozens of priests. One of the oddest religious references I’ve seen in anime so far happens in “Yami no Matsuei” aka “Descendants of Darkness”, where the main villain talks about 17th century statues of Buddha which had crucifixes carved on the back, so that Christians in Japan could veil their faith during times when people were being arrested for refusing to give up Christianity.