Got a PC or a smartphone? Media-sharing sites will let you stream live and interactively. It could be called "self-casting" and it's a whole world of its own. In a single day, via a single site, 100,000 people might be streaming in this way. What motivates people to participate in this form of social media? We go to an annual convention of these live-streamers near Tokyo, and then profile a number of "hosts" we encounter there. They're connecting via such sites with large and small circles of "friends" they might never actually see, let alone meet. It's a new kind of society.