death is swallowed up in victory
General Cross Marian has gone to some time and effort to remove the records on Maria from the Black Order's files. He substituted something banal and plausible, with enough natural irregularities to avoid suspicion. He doesn't like anyone knowing the full scope of his weapons. Not even his presumed allies.
Many of the other Exorcists who knew Maria are dead by now. A high-risk job: it happens: another coffin for the Black Order, another name on the lists of 'fell in the line of duty', another piece of memory gone. Those people who do remember her would probably have said that she was shy (a bit like that new girl, Miranda whatshername) and that she kept herself to herself. They might even have made the joke that Cross always kept her sheltered, and how different was that from the way that she now sleeps in her coffin?
Older Exorcists do tend to have a nasty sense of humour. It goes with the job and with the survival, for as long as it lasts.
General Cross Marian knew Maria, but he could never honestly say that he understood her. She wanted - no, she yearned for - something which he didn't comprehend at all. She desired God, or what she believed was God, more eagerly than he had ever actually wanted anything. While she was in the world, she endured living, and she kept herself from suicide because it would have been a sin, but she sought for her God as a weary man looks for rest at the end of the day.
What he has chained in that sorcerous coffin is her body, nothing more. Her soul is long gone from it. Air moves through the lungs and makes the body sing, just as a musician can command an instrument, but her spirit is gone wherever it is that spirits go. He has enough grace to hope that she found what she was looking for on the other side of death, and that she would understand why he still needs her music.
He knows that junior Exorcists simply assume that her song is "another form of Innocence", a tool that fits the purpose and affects Akuma and humans as a key fits a lock, but they never think to wonder what it is that they hear in the song, or why it so distracts them. They don't bother to go beyond the basic step of comprehension that Innocence is linked to the person who wields it, who gives it form and power in the world. Why he judges, or why another General might create, or purify, or execute.
Maria sang the falling of barriers and the mercy of her God. She sang death as a portal and a release, and her God beyond it: eternal light and grace and pardon, and nothing to be feared. What's left of her song now is shadows and memory, an echo of that voice, enough to make an illusion with.
Cross never believed in her song. Not really. Maybe that's why he can use the song and use her now.
But sometimes it's hard to tell the singer from the song.