The Supreme Court on Thursday dismissed a 47-year-old woman's claims for compensation for emotional distress after her former partner suddenly ended their relationship of about 16 years in 2001 and married another woman.
Thursday's decision by the top court's No. 1 Petty Bench reverses a lower court ruling in favor of the woman, a university professor. The plaintiff and the defendant, a 49-year-old company employee, have two children but do not live together.
The Tokyo High Court had ordered the man to pay her 1 million yen, saying breaking the relationship constitutes arbitrary betrayal of hopes that it would continue.
At issue was whether their relationship was entitled to legal protection, even though it does not go as far as constituting common-law marriage.
Common-law marriages, in which a couple live together like a husband and wife without registering their marriage with authorities, have stronger legal grounds in Japan than such relationships.
The ruling is expected to draw debate on the nature and various forms of marriage or partnerships in Japan, and the rights that couples in such situations are entitled to.
Justice Kazuko Yokoo, who presided over the case, said in handing down the ruling that the top court "understands (the woman's) discontent but cannot deem (the man's) action as unlawful."
Yokoo made the decision by citing circumstances, including their separate residences and livelihood, and the fact that they never lived together or shared common property.