They are audio files, not necessary to play the game. They are the audio version of popular scenes, not just read as they are but ported into scripts for voice actresses to perform, for those interested in erotic audios. They are standalone files to be played and listened to, separately from the game and inspired from it. At the moment, the audio series is suspended, but the support from backers is going back up after the Patreon ban, so I am hopeful they will become viable soon.