"Retro" was the theme at this year's Anime Boston, the largest anime convention in the Northeastern United States, and that idea extended to the event's featured musical acts: veteran pop duo Puffy AmiYumi and 1960s-styled rock quartet Okamoto's.

"The only other time we played in Boston we performed a short set in a musical instrument store down the street," says Okamoto's lead singer Sho Okamoto during our backstage meeting. "We thought we might have 25 people in the hall today, but there were thousands out there."

You can usually find Okamoto's playing top-tier venues in Tokyo. Seeing their name on the roster of an anime convention came as a bit of a surprise, but it shows just how much broader the world of anime soundtracks has become.