This past week, Silicon Valley darling Pinterest, a company that by now needs no introduction, raised a whopping $100 million on a $1.5 billion valuation, and not from the usual West Coast VC’s.

Pinterest followed Facebook’s lead in casting a wider net when looking for big money – Zuckerberg raised nearly $900 million from Russian investors – and picked the Japanese e-commerce firm Rakuten to lead the deal.

Rakuten’s executive officer in the U.S. is the CEO of one of their subsidiaries, a company called FreeCause. His name is Michael Jaconi, and he serves as Rakuten’s liaison to the U.S. tech scene. He agreed to speak with me about the Pinterest deal, his role, and Rakuten’s interest.

Why Rakuten

With Pinterest picking an e-commerce giant for its partner, my mind jumped immediately to monetization, but Jaconi said he’d have to defer to the Pinterest team on that strategy, saying, “right now their strategy is to focus on contiuing to build the service that they’re providing to consumers.”

If Jaconi is right, Pinterest is less focused on monetization for now, and more focused on two things: better user experience, and more users.

That second part is where Rakuten comes in. Jaconi sees their value as helping Pinterest grow not only in the Japanese market, but the other 17 markets in which the company has a presence.

How the Deal Went Down

“Ultimately this was one of the most hotly contested and sought after financings in Silicon Valley in quite some time,” Jaconi said. So how did Rakuten come out on top?

He attributes it to the relationship that formed between Pinterest founder Ben Silbermann and CEO Hiroshi Mikitani. (Read Mikitani’s take on the deal here.) The two men hit it off, Jaconi said, around the idea of a more social  e-commerce experience.

“They both have this firm dedication to creating more social, more interactive, more empowering services,” he said.

I am not a Pinterest user, but the engagement the site fosters does seem more easily monetizable than, say, Facebook. So, what do you think? Is Pinterest worth $1.5 billion?