Singapore-based fund Effissimo, established by former colleagues of Japan’s most famous activist investor, Yoshiaki Murakami, has become the largest shareholder in Toshiba (TOSBF) with an 8.14% stake, a regulatory filing showed on Thursday.
Effissimo Capital Management is closely watched in Japan because of its passing connection with Murakami.
The fund is the largest shareholder in shipper Kawasaki Kisen Kaisha, office equipment maker Ricoh and electronics retailer Yamada Denki.
Get Term Sheet, Fortune’s daily email about deals and deal-makers.
Effissimo’s purchase of Toshiba shares is worth about 65 billion yen ($584.3 million), based on its closing price on March 15, the date of ownership shown in the filing.
The activist fund’s sudden emergence as the biggest shareholder came as the electronics conglomerate is trying to survive through the huge losses stemming from its U.S. nuclear business.
Earlier this month, it missed submitting audited third-quarter earnings for a second time and said it would consider selling a majority stake in Westinghouse which is at the center of its financial troubles.
Prior to the filing, Toshiba shares closed up 6.9% at 207.3 yen.