The group, which is based in Fukushima Prefecture in northern Japan, made its debut in January 2007 with the song “Michi” (The Road) on Universal Music.

The single peaked at No. 39 on the Oricon chart. GreeeeN’s next five singles sold fairly well, but May’s “Kiseki” (Miracle) sold 186,097 copies (downloads and CDs) in the first week alone.

In a month’s time, the song had been downloaded a million times, making it the biggest-selling ringtone in Japanese music history. The band’s subsequent album, Ah, domo. Hisashiburi desu (Oh, thank you. It’s been a while), was released in late June and went straight to No. 1. It has since sold more than 900,000 copies.

What’s notable about the group’s success is that GReeeeN does not perform live or appear on television. In fact, no one knows what the members look like. All four members, known only by their nicknames, were dentistry students at Ohu University when they debuted.

Three have since graduated, but one member has hinted on the Internet that once everyone passes the national dentistry exam and receives their licenses, they may actually appear in public. But in any case they have dedicated their lives to teeth, not music. Their logo is a wide, toothy smile.

Universal has managed to cash in on the GReeeeN phenomenon. Andrew W.K. and reggae star C.J. Lewis, both of whom record for Universal in Japan, have each released single versions of “Kiseki” this past summer.