https://quickandtastycooking.org.uk/articles/ghost-in-the-shell-manyoshi/

When listening to this song, what struck me is that it sounds similar to the choral songs of “Le Mystère des Voix Bulgares”, which was the name of a 1975 recording of Bulgarian folk songs performed by the Bulgarian State Radio & Television Female Vocal Choir. It only became widely known after being re-released by the British independent record label 4AD in 1986.

As it turns out, this is not a coincidence: in an interview, the composer explained he had wanted a chorus in Bulgarian style but using Japanese folk singers. According to the Japanese Wiki, he used only three singers for the recording. The result is a very interesting combination of a traditional Bulgarian mode with Japanese lyrics and singing style.

What is also very interesting is the nature of the song: it is intended to be similar to a traditional Japanese wedding song, but as far as I could gather the composer wrote the lyrics. He used a very archaic style, dating back to the Heian period (794 to 1185, when Kyoto became the capital) or even the earlier Nara period (710 to 794, when Nara was the capital).

공각기동대 오프닝에 나오는 일본 여자 합창이 일본 전통극 양식에 나오는 거라고 생각하고 검색해봤는데 일본에 그런 장르가 없더군요.

그러다가 이 곡이 불가리아 민요 합창 양식을 모사했다는 내용을 찾았습니다. 

들어보니 정말 비슷하네요.