During the time I was living in Japan, there were a few songs that just seemed to take over the audioscape for the year in which it was released. Namie Amuro's "Can You Celebrate?" was the one for 1997, and then there was this one from (can't believe it's been that long) 2003 by SMAP, "Sekai ni Hitotsu dake no Hana" (A Flower Unlike Any Other In The World). It was being played just about everywhere when I was there, and I think wherever it was played, I wouldn't be surprised if friends in a café, a schoolyard or a karaoke box would suddenly just lock shoulders and sing it all together.
Originally, this was meant as a theme song for a Fuji-TV drama titled "Boku no Ikiru Michi"（僕の生きる道...My Path）starring SMAP member Tsuyoshi Kusanagi as a man who, finding out that he has only a year to live, decides to live what life he has remaining to the fullest. However, like a number of theme songs, "Sekai ni Hitotsu dake no Hana" just grew in reputation and popularity to become its own phenomenon.
And why not? It's one of the biggest feel-good songs celebrating individuality I've ever come across. Dark clouds separate, seas calm down, dogs and cats can live with each other again. Written and composed by singer-songwriter Noriyuki Makihara（槇原敏之）as a means of redemption after getting through a dark time in his life following his arrest for drug possession back in 1999, he related that he couldn't credit himself for the creation of one of his most famous songs. Instead, he said that he got the song as a gift from God.
Released in March 2003 as SMAP's 35th single, it hit No. 1 on the Oricon charts for a total of 7 weeks which included 2 stretches of 3 consecutive weeks at the top spot, and it became the No. 1 song for the entire year. Even for 2004, it was placed at No. 11. It also managed to break the 2-million barrier and is currently the 9th-most successful single in Oricon history. It is also included on the group's 5th BEST album, "SMAP AID" which was released in August 2011.
Although Makihara never released his own version of his masterpiece as an official single, he's been getting his fair share of requests at concerts. He seems to be more than happy to oblige.