This is extra conent that will "Unlock" all the songs in the main game of "Touhou Danmaku Kagura Phantasia Lost."
To play songs in the free mode, you have to progress the story or use Dream Drops to unlock the songs.
This extra content will unlock all songs in the main game and playable in the free mode from the beginning.

*You will need to finish the tutorial in the story mode to play the free mode.

More details on the official game page of Unlock All Songs ...