User blog comment:Xilinoc/Ch. 570 (I can't think of a witty title at 11 pm)/@comment-26420452-20140226095129/@comment-5398287-20140226143722

I don't think you have to be Christian to believe in Heaven and Hell. It might've been that he was another religion who believed in similar things, and Kubo just used the Japanese terms for Heaven and Hell so as to not confuse his viewers.