After getting through Gen’s Psync in AI: The Somnium Files – nirvanA Iniative, you finally get the third piece of paper containing the information you need to understand Tearer’s instructions. I’m going to explain how to do it first, in case you’d like to reason it out with a bit of help. Afterward, I’ll just straight up tell you what to put into the text box. I’ll start by saying that this is almost exactly the same as a puzzle you’ve done before, namely the one in the park with the Alfree machine. Here’s what the pieces of paper say:
1 HO ST
2 UN RA
3 IN DG
Thinking back to the Alfree puzzle, you had to look at the pieces and connect them diagonally. You have to do the exact same thing here. Start at HO, then look at letters diagonal to it. Then connect those letters to their diagonal. Continue as if IN DG was above HO ST. Putting them together correctly will give you HORA INST UNDG, which you’ll need to enter into the text box as HORAINSTUNDG. It stands for Horadori Institute underground and gives Mizuki information on something the game pretty much told us during the Ryuki route.
Once you get that entered, then you’ll actually have to go in and find the underground. There’s a puzzle there too, but the game will pretty much tell you exactly what it is if you back out a few times. I guess the testers had trouble replicating musical notes. Granted, as long as you remember the Alfree puzzle, you should have no issue reusing the intersecting arrows to come to the correct conclusion. Unless you find yourself with a convenient case of protagonist amnesia, at least. But then that opens up an entirely separate can of worms. And nobody likes worms.