Continuous relationship since 1951 — The San Francisco settlement
On September 8, 1951, Japan signed the peace treaty that ended the occupation and, the same day, a security treaty that let American forces stay. Sovereignty and dependency were restored in one afternoon, and that pairing is the relationship. The 1947 constitution it rests on came earlier, under occupation, and the entry begins there.
The relationship is usually called the cornerstone of American security in Asia. What is documented: a constitution that came into force on May 3, 1947, under occupation, whose Article 9 renounces war; a security treaty signed the same day as the peace treaty in 1951 and revised in 1960 amid the largest protests in Japanese history; Okinawa held under US administration until 1972 and still hosting most of the US presence; a "sympathy budget" under which Japan pays a large share of the cost of the forces stationed on it — 197.4 billion yen in 2019 alone; and two American shocks delivered without consultation, the 1971 end of dollar-gold convertibility and the 1985 Plaza Accord that nearly doubled the yen. The ruptures ran both ways, and the 2015 security legislation — allowing collective self-defense for the first time — is the relationship being renegotiated from the Japanese side.
This page covers structure, not sentiment. Japan is the section's clearest case of a dependency that both sides chose and both sides have periodically resented. The Plaza Accord is carried as what the documents show — a coordinated intervention with stated aims — and the reading that it "ended Japan's rise" is marked as a reading.