In the simplest terms, Rakuten is the Japanese version of Amazon, everything to everybody. They make a lot of their money simply on their brand name, it costs quite a lot to open an e-store under Rakuten's umbrella. As pointed out they also own a baseball team (part of their marketing strategy). Rakuten means "Easy Heaven" meaning it should be easy and heavenlike to shop on their site. However, anyone who has ever been to Japanese sites knows that their design is simply awful, cluttered, full of small icons, no color schemes etc.
Don't know if it holds up anymore, but for a long time they ware constantly in the top on Nikkei's list of growth stocks.