I feel that the movie is :
I was thinking about famous movies and that's when it struck me that the keyboard represents music, and the gun represents death. When combined, death follows music.
One movie that follows this approach is Inception where, in cue with the music, the characters are killed in the dreams that they occupy, in order for them to wake up into reality after they've completed their respective jobs. This process is referred to as the kick. Meanwhile, the numbers could be related to the time dilation of the dream levels or the minutes they take up in the movie, with the shortest amount going for reality.
Another line of reasoning:
Up until the last part of the movie, the music was what cued the kick. But in Limbo, a gun was needed for Saito to escape limbo.
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