The case was brought by Consul Baron Karl-Gustav Lagerfelt on behalf of the King of Sweden as petitioner for guardianship of Mary Ann Vaughn, the daughter of a Swedish national in Japan, against the Yamaguchi family, de facto custodians of the eight-year-old child, to answer the questions of custody, guardianship and citizenship of Mary Ann Vaughn, also known as Marianne Wilson.
As Vaughn was a civilian employee of the United States, his marriage did not come under the terms of permissible immigration stipulated for US Military Service Personnel who married foreign women (see War-bride).
Due to the absence of recognized civil marriage, James and Vivienne allegedly suffered harassment by US and Japanese authorities.
He received assistance from Patrick McCarran, senator from Nevada, who sponsored private legislation permitting the immigration of Vivienne Joy Wilson to the United States for the purpose of legitimizing their marriage; and recognizing his daughter, Mary Ann Vaughn, who had been born in Yokohama during the interim, as his natural-born daughter.
(81st Congress 2nd Session, v.64 part 2, Chapter 596, Private Law 722, For the relief of Vivienne Joy Wilson and minor daughter Mary Ann Vaughn) However, Vivienne had been weakened by the privations of World War II, and contracted tuberculosis during James Vaughn's absence, during which Mary Ann was cared for by a nanny, Fumi.
The Consul of the Royal Swedish Legation attempted to negotiate a custody settlement with the Yamaguchi family, but was unsuccessful.
According to Fumi Kaneko (reading from her interview in Asahi Shinbun and Shukan Shincho), the baby was entrusted to her by Vivian at her death bed.
There was no mention of a search for the baby; instead Fumi Kaneko said she was the one who approached the Swedish Embassy to recognize Mary Ann before she entered into grade school.
The case attracted considerable attention from the Japanese Leftists, and became a focus of anti-American nationalism in Japan after World War II.