Starting today and ending on Wednesday, ghosts from your character's pasts will show up in Kiseki! Additionally, every island will be covered in fog during the entire event.
The ghosts will basically be mute, floating, incorporeal, rather creepy versions of their "real" selves. They'll show traces of their canon personality, they won't be able to talk, they won't be able to be touched in any way (I know that sounds like a dumb aclaration, but with charas like Nadeshiko or Haruka it seems fitting to clarify that), and won't stay in the same place for long. They'll appear and disappear in different places of Kiseki at random during the entire event.
The fog is, obviously, mandatory, but encountering the ghosts isn't. You can choose to not deal with them at all, you can stick to just the ghosts from your character's own past, or you can have them see both the ones from their and other character's pasts.
I think that's it! As usual, feel free to ask any questions. And if you end up really wanting an extension, please let me know by Wednesday.