Boutique advisers specializing in micro mergers and acquisitions for mostly family-run firms are enjoying a boom as the aging, shrinking population puts the squeeze on Japan's small business landscape.

There are no industrywide figures for deals between ¥500 million and ¥1 billion, but boutique advisers say they are benefiting as owners look to merge their businesses to cope with dwindling demand or as they reach retirement without a successor.

Japan's population, already the oldest among developed economies, is projected to shrink by a third by 2060.