Complex sentence: The Emperor is not the (ceremonial) commander-in-chief of the Japan Self-Defense Forces as in some other monarchies, the Japan Self-Defense Forces Act of 1954 explicitly vests this role as commander-in-chief with the Prime Minister.
Split into simpler sentences: The Emperor is not the (ceremonial) commander-in-chief of the Japan Self-Defense Forces as in some other monarchies. The Japan Self-Defense Forces Act of 1954 explicitly vests this role as commander-in-chief with the Prime Minister.