The meaning of eternal night and immortality/ascension is purely fictitious
God killed God, God fell from then on, the sun disappeared, the world was shrouded in eternal night, and no one became an immortal again.
Every hundred years, Eternal Night City selects six messengers of light among humans and demons to help them ascend. The living see the light, the dead become dust. Humans and demons fight constantly. Only those who reach the top can tear apart the eternal night.