What is Line and why are people going crazy over it?

When the young people of Tokyo want to go shopping, they head for Harajuku. A fabled wellspring of youth culture, the neighborhood offers international retail chains on its main streets and tiny purveyors of bleeding-edge fashion in its back alleys. On this Saturday morning in mid-December, a throng of extremely excited twentysomething men and women crowd into the grand opening of a 1,700-square-foot shop located across the street from H&M and Forever 21. As they enter the store, they’re greeted by two costumed characters: a deadpan bear and an exuberant rabbit. This new store, called Line Friends, is different, to put it mildly. For one thing, it’s not owned by a retailer but by a social media company called Line, which in less than four years has become Japan’s hottest phenomenon by offering an app that provides free messaging and video and phone calls. Those characters are two of the cartoon personalities who live in the app as giant emoji called stickers that Line offers for use when texting.