As Japan gives more say to investors, companies are clinging to a tool that has the opposite effect.

Poison pills, a way to scupper hostile takeovers, are in place for at least 20 percent of firms in the benchmark Topix index. That compares with at least 5.8 percent for Wall Street's Standard & Poor's 500 Index.

Prime Minister Shinzo Abe is seeking to instill more market discipline on Japan's companies by making management more accountable to investors. The lingering prevalence of defense measures suggests a reluctance in the nation's boardrooms to buy into the premier's plans. For Institutional Shareholder Services Inc., the pills are also unnecessary.