Why is NieR's music sung in a language that does not exist?

The idea was director Yoko Taro's, and he explained it on the record: recognisable lyrics in game music can pull a player out of the game, so NieR's songs should sound like a real language while meaning nothing at all. Composer Keiichi Okabe, leading the studio MoNACA team, hired English singer Emi Evans, whose voice he already knew through friends, to sing and to invent the words herself.

Evans's first attempt taught her the problem: mashing random sounds together made every song sound the same. The fix, which she credits to Okabe in her PlayStation Blog account, was system over gibberish. Each song is modelled on one real language, imagined as it might sound after a thousand years of drift. Kaine is built on Gaelic, researched through songs and lessons until its vowels and rolled consonants felt right; other tracks take French, Portuguese, Spanish, Italian, English and Japanese through the same long fast forward. Song of the Ancients, the first she wrote, is the exception that mixes her sources.

Okabe treated the voice as an instrument that must never fight the actors. Because the feature of NieR's music, as he put it in interview, is vocals sung in a fictitious language, even the four versions of the ending song Ashes of Dreams were recorded as four separate vocal takes with different invented lyrics, not one vocal under four arrangements. The result is the rare game score people buy, stream and tour with orchestras on its own: a soundtrack in a language spoken by exactly one singer, in a world a thousand years gone.