Investors in Japanese corporate bonds are increasingly seeking protection against possible credit deterioration when an issuer becomes a takeover target.

Change of Control covenants — which give bondholders certain rights to redeem the debt before maturity if the borrower has a significant change in ownership structure — have until now been very rarely seen in the ¥100 trillion ($680 billion) Japanese credit market. Yet many investors argue that needs to change, with the risks highlighted by future ownership uncertainty of frequent issuers such as convenience store giant Seven & I Holdings and Nissan Motor.

"We need a Change of Control covenant on bonds broadly regardless of their credit ratings,” said Hiroyuki Miyata, a credit portfolio manager at Nissay Asset Management. Investing in yen notes without that has become a risk, he said.