Chinese culture influenced Korea considerably more than Japanese culture, considering historical influence overall.
The three countries that influenced Japanese culture in the Heian period were, India, Korea, and China.
China and Korea
The Asian cultures of China and Korea greatly influenced Japan. These two cultures are close to Japan. Korea has served as a bridge (of cultures) between China and Japan.
Japanese culture was blended with Chinese and Korean culture. Chinese adopted budhism from India which was later spread to Japan. Korean influence can be seen in Japanese paintings and architecture.
China and Korea mostly. China by obvious reasons (Written language and other customs such as the lunar calender, etc. Japanese culture is hugely based off of Chinas) and Korea had other influences as well (Brought over technologies such as paper printing, pottery and art, etc). It's important to note, in the earlier days Korea had more of a direct impact whereas China had more of an indirect one (When Koreans introduced their culture, they also introduced Chinese.) Soon, Japan was able to have relations with China directly
Japan and Korea
Korea because the original people of Korea Migrated to Japan about 1000 years ago. China also influenced japan's culture, with religion and customs.
The Japanese culture has linked blood type to personality for a long time. This Japanese theory is popular in Korea. It is kind of like how some Americans believe personality is influenced by Zodiac signs.
Isolation has contributed to a distinctive Japanese culture, although the Japanese have been influenced by nearby Korea and China
Japan has a long, rich history that spans centuries. In the mid-500s, the development of Japanese culture was impacted by Korea and China. Korean leader Seong of Baekje brought Buddhism to Japan, and Regent to the Empress Prince Shotoku dedicated his leadership to spreading Chinese culture and Buddhism.
China influenced Japan through alphabet and i believe religion. The original Japanese people (The Ainu people) migrated from Korea.
Chinese, Japanese, and Korean cultures share similarities due to historical interactions such as trade, migration, and the spread of religious beliefs and philosophies. These influences have contributed to the exchange of customs, languages, art, and technology, creating cultural overlaps in the region. Additionally, the shared influence of Confucianism, Taoism, and Buddhism has further connected the three cultures over time.