It was the rarest of public appearances. At Toshiba Corp.’s extraordinary general meeting in March, a lawyer, who didn’t give his name, talked for four minutes about why shareholders’ rights should never be infringed.

He was speaking on behalf of Effissimo Capital Management Pte, a secretive hedge fund that had avoided the spotlight for almost 15 years. Now it was coming out into the open, if only slightly, to spearhead a campaign to bring change at the conglomerate — and, by extension, corporate Japan.

Effissimo’s victory over Toshiba’s management in that March 18 shareholder vote was a landmark moment both for Japan Inc. and the hedge fund, whose guarded actions have long been the subject of intrigue.