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.
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.