Part 39: UPDATE 39
Archive 064 - Tsuchinoko reward poster
Compare with Archive 15.
Archive 084 - Tamon Takeuchi's organizer
Archive 086 - Aerial photo of Hanuda village
Note that the layout of the village is in the shape of the Mana Stone.
Archive 087 - "Brain Cell Revival" game
That's a pretty literal translation. Think brain teasers.
After collecting this archive there is an actual minigame available from the title screen. Watch someone else play.
Basically, line up like colors to make them disappear and get points. You can hit a button to add more random(?) units to the board, but they also appear over time.