- Quietus: The Bad End game over music. Starts off with a demented chime, then morphs into a metal, slightly industrial tune.
- Chill and Rigor: Reminiscant of Hello Zepp in Saw.
- Recollection: The piece from the moment in the "Submarine" ending when June talks to Junpei before dying in his arms. It also plays in the True ending when Clover and Snake reunite at the chapel note ; and in the Safe ending when June gives Junpei her final words before disappearing from existence note .
- Octal Game: A much more relaxing piece, contrasting the rest of the tracks tense feelings.
- Morphogenetic Sorrow: A track that clearly tells you that this is the finale. The fact that it plays in the Sudoku puzzle really changes the mood. A remix of it acts as the backbone of the trailer music of the sequel.
- Foreboding: A track that's reminiscent of goldenslaughterer, giving quite an intense atmosphere.
- Unary Game: Guaranteed to induce panic.
- 9 Years: The music that plays during the true ending/prologue. Also counts as Crowning Music of Heartwarming due to the bittersweet finale.
- Ternary Game: An oddly energetic track compared to the rest of the soundtrack.
- Septenary Game: A catchy track that is somewhat upbeat with a tinge of melancholy. It plays in the operating room (Door 7) and the shower room (Door 3) that contains the grisly remains of Nijisaki. A nice break from the usual ominous music.
- Nonary Game. Appropriately for a track that uses the name of the game the characters are themselves stuck in, it plays during the Final-Exam Boss room, and it has the feeling of a "final boss". Even though there's actually one last puzzle beyond this room.
- Senary Game: An extremely dark, yet pumping track playing in several later rooms, setting the mood with its sinister torpedo-shot synth.
- Binary Game plays in the 1st and 2nd Class Cabins, and it's a chipper tune that screams anything but darkness. Contrasts with "Unary Game" a lot.
- Extreme Extrication excels at giving the "escape from the sinking ship" feeling. Very iconic song of 999, though not as much as "Morphogenetic Sorrow".
- Trepidation is the devil of the OST. It plays whenever you find a corpse, and it always goes along with extremely detailed descriptions of the bodies. Scary indeed.
- Digital Root tends to play during scenes that are focused on lore or backstory, or when one character is explaining something to another. Its opening notes, which set a calm mood, are easily recognizable, so it can be identified as a recurring motif even after just one run through the game.
Awesome Music / Nine Hours, Nine Persons, Nine Doors