This is Clerodendrum bungei or more commonly known as rose glory bower. Its bright pink buds are so pretty (1st photo) but the pale pink flowers (2nd and 3rd photos) are also beautiful! So, what do the in-betweens look like? The answer is the 4th photo, i.e., only one flower is open with the remaining being still buds.
The plant usually produces flowers in late summer although it's still June but it's understandable. The rainy season, which started in Tokyo in early June as usual, is expected to end this week, three weeks earlier than usual. This means a terrible Japanese summer, which is hot and humid, has started😂!! It was 35°C (i.e., 95°F) yesterday!!