Answer:
The sharp slim blade, that cuts the wind.
My first is second in lineอพ I send shivers up your spineอพ not quite shining bright I glitter in the light.
I open wide and tight I shut, Sharp am I and paper-cut fingers too, so do take care, I'm good and bad, so best beware.
Feed me and I live, give me drink and I die.
They're up near the sky, on something very tall. Sometimes they die, only then do they fall.
What is always coming but never arrives?