Ume apricot is a symbol of the Tenmangu Shrines, so many ume blossoms can be seen in there. Tenmangu Shrines are Shinto shrines where a historical hero "Michizane Sugawara" is enshrined. He loved ume blossoms very much.
Shinto is the indigenous religion of Japan. It is polytheistic, and its gods are worshiped at shrines.
It is based on nature worship, hero worship and ancestor worship. It has neither a specific founder nor any books of scripture.
This bonsai tree has both red (pink) and white blossoms. I don't know how to create it, but it takes long time and energy to make it.