The "Drakengard" main series in order of original release:
Drakengard (2003, Playstation 2)
Drakengard 2 (2005, Playstation 2)
Drakengard 3 (2013, Playstation 3)
NIER (2010, Playstation 3/Xbox 360)
Drakengard: You're a villain.
Drakengard 2: You're a hero.
Nier: You think you're a hero, but you're really a villain.
Drakengard 3: You think you're a villain, but you're really a hero.
Nier Automata: You're not really sure what you are, of what you are doing, or what the end result of it will be.