After the firefight in the gas pipes area near the exit point of the map, there will be a gas pipe on fire. Turn the object off in the next room, then return to the now extinguished pipe area..There is a semi secret walkway there. Walk in, find the ladder, and climb up. You will find a health booster, and there is a door on your left. Go into that office. Listen to the song. It is the main theme from Shogo: Mobile Armor Division. An anime FPS created by Mololith. Look at the dry marker board. It is the same one from an office level from Shogo: Mobile Armor Division.