Japan’s legal sources do not support the statement that Tokyo is the de jure capital. The only law that explicitly used capital-city language for Tokyo was repealed, and later laws define a capital region around Tokyo without legally naming a capital city. Tokyo is the de facto seat of government and is commonly called the capital, but that is not the same as current formal legal designation.
Caveats
Do not confuse de facto capital status with de jure status; Tokyo clearly has the former, but the legal basis for the latter is absent.
The 1950 Capital City Construction Law is no longer in force, so it cannot establish Tokyo’s current formal status.
Foreign references and common usage often call Tokyo the capital, but they are not authoritative on Japan’s internal legal designation.