・Digital Artbook: contains the game's key arts, stage concept designs, character designs, and the lore from the game.
・Mini-OST: contains 15 sound tracks from the game with its attractive atmosphere.

This content is available through bundle purchase with "GetsuFumaDen: Undying Moon Digital Deluxe Edition - not sold separately.

More details on the official game page of Digital Artbook ＋ Mini-OST ...