This amazing derailleur is an off-the-shelf Shimano 105 (5800 L SS) derailleur that has been refinished with a very fetching 'Cherry Blossom' design.
The repainting was done by Kakiku RE Bicycle Workshop, based in Fukuoka, Japan. They appear to have decorated a number of Shimano components, and even groupsets, with this design. They may, possibly, also offer other designs.
The 'Cherry Blossom' or 'Sakura' motif has a long history in Japanese art. It is associated with an appreciation of the fleeting nature of life, with hope and rebirth and with friendship and goodwill.