It's actually amaranth... I'm pretty sure Mike said it somewhere, but I'm tired, I may be thinking incorrectly. But it DEFINITELY sounds like amaranth, so I go with that.
An amaranth is a purple flower, and also a legendary flower which never wilts. What the lyrics say is that the narrator has kept this symbol, the undying flower, as a means of when they will be together (again). When they both walk the shadows, it will set ablaze, and vanish. But... it NEVER sets ablaze and vanishes. So they will never be together (again).
At least that's my view. Black Rose Immortal has... awesome lyrics.