Traumend, episode 6: a chanting song before Suigintou finds Barasuishou

There is an absolutely beautiful song that plays while Suigintou is flying around her N-Field where Bara is lying in wait. It happens around the middle of the episode.

This song is not on any of the soundtracks, and it seems to go entirely uncredited: everywhere.

Anyone have any information on the artists? I know it is a japanese duo that sings it.