I see an interesting patern lately on Kajiura osts. While before it was kinda mixed vocalists now she started assigning vocalist to project.
SAO = Remi
Heaven's Feel = Kasahara (and a bit of Remi)
Kimetsu = Chiaki
El Melloi = Hanae
hi buddy george1234, sorry but i didn't get the meaning where is the link for the soundtrack. XD
It has possitives though, if she's good vocalist they can have more vocal combos and the 3 of them would get less lines = less tired
A fourth member doesn't necessarily have to be Maya. Although personally I think adding a fourth member would be a mistake at this point, the Kalagirls have been together for ten years now and developed a very close relationship between them, so an extra vocalist would just be weird.