an MP3 saga is an ongoing fanmade story made by one or several people and released through many episodes. It's all audio files, hence the name, "MP3 saga". All the fictive characters are fully voiced, often by the creator himself and his friends. It can be a very rich and complex story with lots of things happening, lore, backstories, twists, etc. There's also music/OST for the episodes, often composed by the creator himself, like in this case. The first episode of Damien's MP3 saga, "Erebys", is on his youtube (https://www.youtube.com/watch?v=8y0RboBEHnw) and there's even an "episode 0" prior to that upload, which I assume tells more backstory about the premise or the events that led to the story. He's also uploaded a few of the OST tracks already, including Tourments. If you're interested, the synopsis from the description says: "Luna, who is back, struggles to live peacefully with the others feeling hostility toward her. Is the past repeating itself?" so it sounds like it's a darker interpretation of what happened after Luna got back.