most of the lyrics are not that hard to figure out...well maybe compared to popular music but I compare them to figuring out classical poetry because the lyrics are pretty close to it.
a quick version of what i've found Black Rose Immortal to be about: He is calling, looking for someone that was lost and cannot find them. His spirit has wavered in the face of this and all possible paths have been travelled, he has given up hope and laments for what is lost. Nothing is around except the night/emptiness, he is as a shadow and can only watch from darkness. He remembers the search for what he lost and how difficult the search was, then the moon breaks the darkness. We finally see him, he seems empty, and he enters a place..not really sure what...but the world is empty and cold. He sees who he was searching for, and no words are spoken as they wait for the sun to break the cold/dark/emptiness. The birds fly off and shadows leave with the coming of day. He seems to not want to be reminded of the lonliness endured while, well we assume now it is a person, a love, was gone. It seems she is still far away, very vague and dim, not quite real. More a thing of dreams maybe, and yet he still treasures her. Now we find that she died, followed the moon, as her soul "followed the divine herd" into the sky. He kept a token given to him, Amaranth is "an imaginary flower which never fades". Hence the rose, his love which never fades even in death. The whole story is a sort of dream for what was lost. He will keep it until they are joined in death, eventually it will burn away as well...maybe when they are joined. In any case the symbol, their love, is the black rose immortal. Then things become dark again, daylight fades, the story is over and even nature seems to mourn the loss and that he always dreams of it...which is what just happened.
to me it fits quite well into To Bid You Farewell....anyway its just my interpetation.