Because Takaakira's house was on the side of Saikyu (west part of capital), which was unusual at the time, he was also known as 'Saikyu Sadaijin,' from which the book title was derived.
高明邸が当時では珍しく西宮（右京）側にあったことから、「西宮左大臣」の異名で呼ばれ、書名の由来となった。