Japanese e-commerce giant Rakuten confirms today that it lead a $100 million financing round for Pinterest, the image-oriented social curation site. The investment values Pinterest at $1. 5 billion, according to the Wall Street Journal, which is half a billion more than Facebook paid for Instagram just a couple weeks ago. Together, that’s $2.5 billion for a pair of companies that don’t have a single business model between them. In an interview with the Financial Times, however, Rakuten CEO Hiroshi Mikitani made it clear he sees in Pinterest an opportunity to create a new model of social-discovery driven e-commerce. Your move, Amazon.