Kukai trained, and researched the Buddhism. Kukai read the sutra esoteric Buddhism "Dainichi sutra".
However, because the content was very difficult, he did not understand the meaning.
He wished that he went to China that was the advanced country of esoteric Buddhism and studied.
When he passed 30 years old, he was chosen as one of Japanese envoy to Tang Dynasty China in 804.
He went to China by the promise to study for 20 years.
He took the end and one month or more of a painful voyage of disregarding, traced to China by the life, and was able to attach.
However, because he had not had the document that proved it was Japanese envoy to Tang Dynasty China, landing was not permitted.
Then, Kukai wrote a letter to the government official in China.
He was trusted because these letters very wonderful were sentences and characters, and they were able to enter a country in China.
Kukai arrived at the capital of China.
To learn esoteric Buddhism, he studied Sanskrit (word of ancient India) and an Indian Buddhism. The leader of esoteric Buddhism at that time was KEIKAKASHO priest in the blue dragon temple. And, he became an apprentice of the KEIKAKASHO priest in the blue dragon temple.
Kukai learnt esoteric Buddhism from the KEIKAKASHO priest.
And, the KEIKAKASHO priest gave Kukai the name of "HENJOKONGO". "HENJOKONGO" is a meaning "Uppermost person who universally shines on all of this world".
The KEIKAKASHO priest gave Kukai the tool used for the ceremony of esoteric Buddhism, the sutra, and the mandala (The mandala: one that the world of the Buddhism was shown in the picture).
He left a message, "Please return to Japan early for people's happiness and make esoteric Buddhism known", and died.
Then, Kukai returned to Japan with Japanese envoy to Tang Dynasty China in 806.