Anime treats Christianity about as seriously as it treats Buddhism or any other faith, which is to say not at all. There are comedic takes like Saint Young Men, some exorcist stuff like Vatican Miracle Examiner and the priest character in Ghost Hunt, and occasionally someone will take a look at the history of Christianity in Japan (for instance, the Christians Arc at the beginning of the third season of the original Rurouni Kenshin). If you're looking for something that's Christian in philosophy, you aren't going to find it.