Many conservatives refer to America as a Christian nation (though that’s a point that can be argued). Japan, most certainly is not such a nation. Culturally and religiously, Shintoism and Buddhism form a syncretic mix that affects the daily (and even minute-to-minute) lives of most Japanese.
Therefore, it’s no surprise to see one or both traditions play a major role in some anime. Buddhism is ever present in Natsume Yuujinchou, as attested to in one of my favorite blogs, Major Arcana. See Aorii’s write-up about this by clicking the link below: