Chief Cabinet Secretary

The is a member of the cabinet and is the leader and chief executive officer of the Cabinet Secretariat of Japan. They are also a member of the National Security Council, and is appointed by the Emperor upon the nomination by the Prime Minister. 
The Chief Cabinet Secretary is the second in line of succession to the Prime Minister, unless the office of Deputy Prime Minister is being used. 
Since 1947, the office of Chief Cabinet Secretary has been seen as the job to have before wanting to become Prime Minister. The first Chief Cabinet Secretary to become Prime Minister was Ichirō Hatoyama. Since then, eight other former Chief Cabinet Secretaries have become Prime Ministers, most recently Shinzō Abe, Yasuo Fukuda, and Yoshihide Suga.
Yoshihide Suga, who later became Prime Minister of Japan, was Chief Cabinet Secretary under Shinzo Abe for almost eight years, making him the longest-serving Chief Cabinet Secretary in history.