Sky, Empty
What was the biggest hole in the construction of the world? The sky. If you think about it, the sky is like a big hole someone forgot to fill in. That's why this kanji also means empty! Makes sense — nothing is more empty than the sky.
Next time you look up at the sky, try to imagine it's a big empty hole you're stuck at the bottom of.
くう
そら, あ, から, す
None
The sky is usually empty until clouds stage a coup (くう). Basically you can think of the sky as the site for one coup after another as the weather changes.
First the sky's cloudy, then it's clear and empty, then overcast again... Just coup after coup!