AI: THE SOMNIUM FILES - nirvanA Initiative (JP)

in the finale of the game, you'll be running around to every location talking to all the characters in the game. eventually, you get to naix headquarters and talk to tokiko's hologram. she will tell you the nil number. this number is different for every player, so write it down.
then when you load up the game again, go to ryuki chapter 1, "ought to know", and go to the naix president's office. finish all dialogue options and check the symbol on the back wall. after this, she will ask if you are a frayer, answer yes. then she asks if the world is fictional, answer yes. then she will ask you for the nil number. type it in. hit enter and get ready for a trip. you can walk straight through the wall with the symbol to find tokiko outside the world and talk with her. choose to share the info with ryuki.
after that it's just straightforward talking to everyone until you reach the end and the achievement pops