The reason we have a NieR crossover raid series in Final Fantasy XIV is because Naoki Yoshida got Yoko Taro and Yosuke Saito drunk. Seriously; he tells the story about plying them with good steaks and bottles of wine before springing the question of working on the game with them. This may seem a little inappropriate, but considering that Yoko Taro is a legendary creator troll and would also get yelled at by the FFXIV team about having the player character take actions which were inappropriate, perhaps it’s also the most fitting way to start the story.
Yoshida explains that the motivation was in part borne from fan requests to do some sort of crossover between the two games, explaining that he wanted something much more substantial than simply tossing the costumes from NieR: Automata in FFXIV. Taro also explains that while the story was something new to him, having never worked in MMOs before, it’s a story he’s proud to have worked on specifically because it’s so different. Check out the full interview just below.
Source: YouTube