So I was listening to The Contract, and I was finding the meaning of the chorus extremely clear. I'm fairly certain it describes the conditions of "the Contract": control and resurrection. "Submit yourself to me / Your body and your mind; give it willingly” suggests that the speaker will gain control of the subject, in exchange, the subject will “come alive again”.
I found that this theory shares some parallels with some other songs. Shi No Barado, for example, contains the submission elements. “Cause baby you can use me / I will do what you want me to”. As for the revival part, the title does translate to “Ballad of Death”.
Euphemia also seems to refer to the same event. “I became your puppet master, / As you stared into my eyes”. I doubt the line “Oh hold me closely and die in my arms” refers to the same death the contract seeks to undo, due to the difference in tense between the two (The becoming of the puppet master is past tense, the death is present). However, there is no confirmation that each song is spoken at the same point in the timeline of the story.
In summary, the subject dies and is offered a chance at life if she (I believe she is female, possibly Cassandra) is controlled by the speaker. This revival could be the same event talked about in the upgrading theories, see Override Symphony and System;Start, which would make the subject most definitely Cassandra, based on 11/11 11:11.
It's also mentioned in The Contract that the subject tries to "Smile away your debt", and in The Strays that "You can outrun everything but the debts that you owe", so I think this "contract" is eventually broken or left unpaid by the subject, whether by dying or disobeying.
After hearing in Override [C] "But you survived the override", I think the breaking of the Contract involves the idea of "The Ghost in The Tape" (Override [A] and The Tape). Basically, the submission aspect is broken, as Cassandra disobeys. I think the Ghost is what the speaker calls the remnant of her "Free Will" or similar concept that lead to the rebellion, breaking whatever control he had; his "plan mislaid" (The Life of a Ghost).