Secret Messages

 are writings left behind on the walls by other human beings and scattered throughout all the locations in. The messages are not visible to the naked eye and only appear when illuminated by the Special Flashlight.

Background
Seto first encounters secret messages in the Azabudai Station Mall, shortly after picking up the special flashlight. In order to find the missing Star key item and continue his search for the silver-haired girl, Seto follows the trail of secret messages further back into the mall.

Though it is not stated true, it is theorized that the authors of the messages are, like Seto, possible survivors of the Glass Cage Project, as many messages contain references to "survivors" and preternatural creatures. However, the survivors spoken of could refer to those that survived earthquakes or other natural phenomena.

List of Secret Messages
Below is a list of secret messages grouped by the location they are found in.

Twilight Tower
N/A

Trivia

 * It's unknown whether the secret messages are caused by the Glass Cage Project since all of the implied writers of these messages are either dead, AI (Crow), or a "planned child" (Ren); or they're hidden for another reason.