This is a manga dedicated to making an immortal person suffer the most horrific torture and pain imaginable, simply to arouse people who get off on human suffering and torment.
No, literally, that the plot and intention of this horrorfest.
It has no moral, it has no other goal, it is "Torture for the sake of torture", to quote O'Brien from Nineteen Eighty-Four. It's only purpose is to shock and horrify, and for those who actually get off on shock images, masturbation material of the most depraved kind.
Only read this if you want to see some of the true depths of depravity played for the most bastardized form of "titillation", assuming watching a young woman be tortured, mutilated, and otherwise forced to endure depravity that would make the Nazis vomit gets you off.
Otherwise, stay the hell away from this work, if you want to keep your sanity and retain a shred of faith in humanity.