Demon of the Opera

(This story is the fan fiction that shall explain the birth and life of Sebastian Michaelis before he became the demon we all learned and grew to love from Kuroshitsuji.)
Back in 1817, London England, it was said that the newly built Opera House was haunted by an impure spirit. He has been there for decades before the building was built, but no mortal knows the truth behind the creature who lives beneath the Opera House...
One courageous young woman and her younger brother years later (1860) investigate this mystery that England urged to learn about. Although the many dangers that she, her brother, and the performers are put through in order to keep his secrets unknown, she soon finds out that he is a monster who will help seal her insightful fate in order to save her young brother whom she holds dear, but in order to save him, she must sacrifice the most precious item known to mortals, and willingly give it up to this dark and ominous creature forever...
Will she ever see the light of day ever again, or will she dwell in the darkness forever?