As a university student, Mr. Su had taken to Marxism and lived in China, where he assisted Mao Zedong’s revolution for more than seven years. But after Mao triumphed in 1949 over nationalist forces led by Chiang Kai-shek in the Chinese civil war, Mr. Su abandoned the Communist Party that sought to recruit him.

The reason, he said in an interview in March, was that after witnessing countless executions of Chinese by Communist forces, he realized that their true ideology was not Marxism but rule by fear.

“Why should you need to kill so many people to move things forward?” he asked.

He returned to Taiwan. No longer a Japanese colony, it had become the new base for Chiang’s vanquished Republic of China government, now ensconced about 100 miles from the mainland across the Strait of Formosa. Taiwan had also entered what would become a nearly four-decade period of martial law known as the White Terror, under which Chiang’s party, the Kuomintang, arrested and tortured more than 100,000 people and executed more than 1,000.

Determined to overthrow the Republic of China and establish a Taiwanese state, Mr. Su and others drew up plans to assassinate Chiang, who had become a Cold War ally of the United States. But in 1952 their plot was discovered, and Mr. Su stole away to the northern port of Keelung, where he made his escape to Japan on a boat exporting bananas.

In Japan he reunited with his girlfriend, Hiraga Kyoko, whom he had met years earlier in China. Months later, the couple opened a restaurant, New Gourmet, in Tokyo’s Ikebukuro neighborhood. (The restaurant still operates, under different management.) He continued his underground operations from Tokyo, training Taiwanese revolutionaries in the guerrilla tactics he had learned in China.