Make
The leader's key is the key that makes all the other keys. It's sort of like the one ring to rule them all, the one ring to bind them... except with keys.
Imagine the leader taking his key to open up a safe that has a button to make other keys for the underlings. No key is as great as this key, though.
さく, さ
つく
None
The leader makes all the keys and puts them in a sack (さく) to distribute them to the underlings, who then saw (さ) them into shape.
Imagine the leader making the keys and dropping them one by one into a big sack. He's always walking around carrying a big sack over his shoulder, distributing the keys to his underlings and watching them saw them into shape.