Miyoko Watai, 59, is the acting president of the Japan Chess Association and involved in a romantic relationship with Fischer, 61, the New York Times reported Friday.
"I could be a sacrifice pawn," she said. "But in chess, there is such a thing as pawn promotion, where a pawn can become a queen."
Fischer's lawyer said the engagement formalizes an authentic bond of love that has already been established between Fischer, a former world chess champ, and Watai, a four-time woman's chess champion in Japan.
"It was a de facto marriage; we are now making it a legal marriage," lawyer Masako Suzuki said. "I have never seen a case where there is this passion and devotion."
Fischer was detained July 13 because the United States ordered the revocation of his passport in December.