Record shareholder activism is combining with rare hostile takeover bids in Japan, in a trend that's seen as good news for investors in the country's ¥675 trillion stock market.

Activists such as Elliott Management Corp. have been snapping up shares in targeted firms and agitating for a higher price. At the same time, corporate Japan itself has also become involved in the battles, making unsolicited — and opportunistic — offers for peers.

In the latest example on Friday, Hoya Corp. offered to buy NuFlare Technology Inc., seeking to thwart Toshiba Corp.'s earlier proposal to take full control of its listed affiliate. A fund linked to famed homegrown activist Yoshiaki Murakami sits on NuFlare's shareholder register. That comes as a high-profile tussle for control plays out at the developer Unizo Holdings Co., which also features a mix of shareholder activism and potentially hostile bids.