Premise: Masako Sen (千容子 , Sen Masako , born 23 October 1951) , formerly Princess Masako of Mikasa (容子内親王 , Masako Naishinnō ) , is the fourth child and second daughter of Takahito, Prince Mikasa and Yuriko, Princess Mikasa. She married Soshitsu Sen on 14 October 1983. As a result, she gave up her imperial title and left the Japanese Imperial Family, as required by law.
Hypothesis: Japanese law did not force Masako Sen to relinquish her royalty.