The King and the Boy Have a Secret.

Umeichi Kousaka is known as a young genius in the world of Japanese-style painting. However, he is also known for his fearless and haughty personality which has earned him the nickname "King." One day, a young boy named Hikari suddenly appeared at Kousaka's house. Hikari doesn't have a place where he can be himself in neither his school nor his home. He is also totally afraid of everything around him. Then one day, the two met with an accident after which they found that they have swapped bodies? (Source: Kodansha, translated)