Agatha is a dark angel.
Angels are beings that are created to obey, to carry out the will of their master without questions.
And like other angels like Agatha, whether they serve the light or the darkness, this dark angel serves in blind faith.
There's no escaping the master...there's no escaping the wailing of victims either.
Whether Agatha hears them or not, whether they are seen or not, this angel knows they will continue to haunt the one who have slain them for all eternity.