The Forest Note is an item exclusive to the Bloody Brief of a Beckoning Bulletin mystery. It is acquired by completing its sidequest (Investigate the Forest twice), and it is required to achieve Ending A. It seems to be a suicide note of someone under the malicious influence of Together. It contains the following text:
"I write this for everyone wanting to stay behind.
The sacrifice is worth it. Life's meaning comes from our relationships. Share death, and that connection will outlast you.
There won't be anything left but US.
Everyone here is waiting for you so if you lose your resolve
just listen to the VOICE OF HUMANITY"
During the mystery's final investigation, having acquired the note will enable an additional option called 'REMEMBER THE FOREST NOTE' in the computer's second screen, which, in turn, will enable three other options. See Bloody Brief of a Beckoning Bulletin for more information.