Kazuya Kamenashi
Together with Kazuya Kamenashi, Yamashita released the single "Seishun Amigo" in November 2005. The single was the soundtrack for the drama "Nobuta wo Produce", starring Kamenashi and Yamashita, and it topped the Oricon yearly charts in 2005. "Seishun Amigo" eventually sold over 1.5 million copies and is Yamashita's best-selling single to date.