Snapping back to attention, Mu You continued his search, having just found two clues.
[You continue to search as directed and finally find a broken Octave Box hidden behind the window sill.]
[You open the Octave Box only to find that it is empty.]
[Obviously, you're a step too late; whatever was inside has already been taken by someone.]
"Huh?"
Mu You was taken aback; the second clue had unexpectedly hit a dead end.
Adding this to the 'footprint' hint from before, it seems someone really had been in here before and had found the diary inside the Octave Box ahead of him.
Apart from him, the only other humans that could freely access this abandoned area were obviously the 'Administrators'.
[You realize that it was possibly an Admin who got the clue before you.]
[Judging from the footprints on the ground, this person is a woman. Among the female administrators you have encountered in this underground factory, there is only one, the elderly lady in green with the bifocals!]