SQUARE has also posted an official synopsis of NieR: Automata’s story:
Players will play as 2B, a battle android. 2B is a member of an infantry squad, YoRHa, equipped with a sword and the “Pod” support system. The game will tell the story of 2B and two other androids, 9S and A2, as they try to save a dystopian world overrun by weapons called machine lifeforms.
NieR: Automata was announced at E3 in 2015 and will feature such talent as Yosuke Saito, known for his work on Dragon Quest X, as the producer, character designer Akihiko Yoshida from CyDesignated, Inc., and TEKKEN composer Keiichi Okabe from MONACA, Inc. The game has not been rated yet, but judging by its predecessor’s rating, it will likely be rated M as well.