Square Enix explains the various connections between NieR Replicant and Automata, including the various cameo appearances between games.

Automata saved the Japanese games industry. According to Yoshida, the game was so well-received and so unequivocally Japanese ...

The adaptation features extended battles, touches on characters' backstories, and integrates elements from NieR Replicant ... fighting 2B and 9S as the final boss of Route A/B.