Hikaru no Go, a popular anime and manga that revolves around the game of Go, an oriental board game that has been around since ancient times.
Fujiwara no Sai, the one with long hair, is a spirit and a Master Go Player. He has not yet moved on to the next world because of his strong desire to play Go and accomplish “Kami no Itte” - “Divine Move,” or the “Hand of God” a perfect game.
Shindo Hikaru is the only one who can percieve Sai, and therefore is the one that Sai continually pesters to play Go with! Though at first, Hikaru has no interest in Go, his passion grows as he begins to understand the game the more he plays.
It’s probably one of the most influential animes / mangas Japan has seen. And the cosplay attempts of the series says a lot, as well as the rise in the number of Go players around the world.
Image originally from the Anime Illusions Forums.