Hard pick because I listen to a game or series for a while, then another. Just today I went and listened to a lot of Sonic tracks, which I do once every few months. I guess Atlus games (SMT, Persona, EO), Metal Gear Rising, Ace Attorney, TWEWY are in the lead off the top of my head, but after a month I might give a different answer. My relaxing music playlist is mostly the official classical arrangements of Etrian Odyssey 1+2, so let's go with that.