Ryuu means Dragon Spirit in Japanese. According to dragon mythology, this serpentine creature protects Buddhism. The dragon is benevolent and just; bringing good fortune and wealth. They are powerful and fearsome but never malevolent.
Considered deities in India, they protect Buddha. Even before his enlightenment “snake-like beings resembling clouds” protected Siddhartha from wind and rain for seven days. (Above paragraph adapted from book by M.W. De Visser.)
In China, dragons were depicted centuries before the introduction of Buddhism in the 1st and 2nd centuries AD.