In between the seventh and eighth centuries C.E. Japan was influenced by Chinese cultural in many ways other than Korea and Vietnam were. For example china had a major impact on all three civilizations however Japan was the only one that didn’t get conquered unlike Vietnam and Korea. Japan was also much farther away from china than Korea and Vietnam were.
Japan was influence by china in many ways, for example japan began to barrow Confucianism, Language, Buddhism, Chinese art & architecture, and not to mention Chinese government structure. In 646 the Japanese emperor introduced administrative reforms, the Taika reforms, which intended to remake the Japanese government like a Chinese model.
On the other hand, Korea and Vietnam were much closer to china, which made it easier for china to conquer them. When the Han invaded Korea it split into 3 kingdoms the Koguryo, the Silla, and the Paekche. Koguryo adopted Buddhism, the Chinese code of law, the taxation system, and the bureaucracy. The Silla military followed a code combining Chinese belief systems (Buddhism and Confucianism). Last, the Paekche adopted some Chinese styles for their art and architecture, but their styles were still unique. The Koreans also adopted the Chinese writing system. The Vietnamese on the other hand saw the benefits of China's technology and achievements, but felt the need to preserve their own identity and didn't want to be swallowed by China's culture. Vietnamese culture was very different than that of the Chinese, and had its own distinct art and literature.
Finally, while all the civilizations were influenced by china they were all influenced in their own unique way. For example Vietnam and Korea both got conquered unlike japan due to the location. As they all learned many things from china they were all beneficent from the importation of Chinese culture one way or