The emperor, Takeda said, was valued "not because he is intelligent or handsome."
"It's because he is the inheritor of the blood that has been preserved for 2,000 years," he said.
Other opponents add genetics to their argument. Since women have two X chromosomes while men have an X and a Y, the imperial throne's male line has preserved its Y chromosome intact.
"Maintaining the male line is the condition to preserving that Y chromosome," said Hakubun Shimomura, a lawmaker for the governing Liberal Democratic Party, who is one of the leaders of a campaign to reject the panel's recommendation.
"The bloodline is important for the emperor to be a symbol of the nation and the unity of the people," Shimomura added. "This symbolic imperial throne preserves Japan's culture and tradition in total. The imperial throne is Japan itself."
Like many other opponents, Shimomura does not oppose Princess Aiko's ascension to the throne, as long as a male with the right Y chromosome will succeed her. Princess Aiko would be a "pinch hitter," he added, the same way the previous eight empresses had been.
But where to find the right Y? During the US postwar occupation, two groups that had ensured male heirs over the centuries were abolished: other imperial branch families, like Takeda's, and concubines, who are said to have given birth to about half of past emperors.
Reacting against the panel, a cousin of the emperor, Prince Tomohito of Mikasa, 59, wrote that those two groups should be resurrected to maintain male lineage.
"I wholeheartedly support it," the prince wrote about a revival of the concubine system, "but I think that the social mood inside and outside the country may make it a little difficult."
"Unless we carefully hold and express opinions regarding 2,665 years of history and tradition, we'll move in the direction of changing Japan's `national essence,'" the prince said. "Furthermore, one day, arguments that the imperial system is not needed will even emerge."
But some supporters of the panel's recommendations say that a female line would bring badly needed equality to a society where a woman is still expected to join a man's family upon marriage, take his family name and be buried in his family's grave.
For most of the throne's history, emperors lived quietly in Kyoto. But during the Meiji Restoration of the late 1800s, as Japan tried to modernize and catch up with the West, Emperor Meiji was brought to the forefront to try to unify Japan; his grandson, Emperor Hirohito, who died in 1989, was considered divine until Japan's defeat in World War II.
Mikiyo Kano, a professor of women's history at Keiwa College, said that after Meiji, the emperor and his wife were held up as models for the Japanese. Starting with Meiji and until Japan's defeat, emperors dressed in military uniforms, while their wives promoted the Red Cross and patriotic associations.
"I think the male succession system in the imperial family has led to the discrimination and oppression of women in general in Japan," Kano said.
A female line would make a woman the symbolic leader of the nation and show a man deferring to her, as wives of emperors do.