itch.io

It has been a while so I do not remember fully. I am 100% sure i described it in the walkthrough, though. It is linked in the OP

After you try to assign the event to Nyx, go and chat with Gwynn. This will launch a mini-game for the map.

The game is a sliding-tile thing where you have to connect the two ends of the path. You can also get bonus items by matching rubble tiles, and use action scrolls to get more rubble to work with.