From Viz:
Humanity, having faced extinction at the end of the 20th century, would not have entered the new millennium if it weren’t for them. In 1969, during their youth, they created a symbol. In 1997, as the coming disaster slowly starts to unfold, that symbol returns. This is the story of a group of boys who try to save the world.

Note: Won the Kodansha Manga Award in the category "Best General Manga" in 2001, the Excellence Prize at the 2002 Japan Media Arts Festival, the Shogakukan Manga Award in the "General Category" in 2003 and the first ever Angoulême International Comics Festival Prize for a Series in 2004. It also won the the Grand Prize at the 37th Japan Cartoonists Association Awards, and the Seiun Award in the Comic category at the 46th Japan Science Fiction Convention, both in 2008 and Best U.S. Edition of International Material at the Eisner Awards in 2011 and 2013.