Alright, the year is 2024. I'm a 28 yo old french catholic. I know kyrie chant since I was born but this version sounds more medieval and never heard it after even from protestants or orthodoxes.. I think it's a japanese like theme. Heard a lot of similar stuff with the "pain" (not bred) theme or other, in anime from the early 2000's. Full gothic but not really, happend to me playing xenoblades chronicle 2 too (what a soundtrack). Took me 28 years to recognize a song I thought was meh in a theme I adore.
OH MY GOSH no way. Im an orthodox christian and i just realized this song is "Christ is Risen", probably the most quintessential orthodox song. It was made hundreds and hndreds of years ago. Wow, i cant beleive i didnt notice this while watching the show. Must have been so caught up in the plot.