(Un)Reasonable discrimination in family-related issues: a cleavage between the Japanese Supreme Court and the civil society

The Japanese Supreme Court frequently resorts to adjudication techniques, such as the reasonableness test, common to Western courts. Nevertheless, it has an extremely low rate of unconstitutionality decisions, proving to be deferent towards the two other branches of government. An explanation comes from the case law dealing with the principle of equality and the (un)reasonable discrimination, mainly in family-related issues. The JSC moulds the reasonableness test after the traditional Japanese values and traditional family system centred on the household, thus upholding the challenged provisions. The 2015 and 2021 decisions on Art 750 Civil Code (the spouses have to adopt one surname) are a good example of how the JSC employs reasonableness and of its deference towards a conservative Diet. By analysing the most relevant case law in family-related issues, the paper claims that a deferent court and an inactive Diet deepens the cleavage between the civil society and the institutions.