XIETIAN
Eternal Bitterness + Feng Tian Wu's fire focused power = Fire Sorrow The reason why Fire Sorrow was looking for Sirius (who was presumably related to BZ at some point) might be because of her regret and longing (born from the passing time). Fire Sorrow was said to come from the same world as Lucifer and Sirius, sooooooo if we assume the current world where it all took place was way before the oldest Higher Existences become Higher Existences (their original world) then the current world might be the Origin World or The World Where It All Started. this are only fragments so far and I could be wrong, let's gather more info's! I'm excited to where this story would take us