Born in Edogawa, Tokyo on February 23, 1986, Kamenashi is the third child of his parents. He has two older brothers, Yūichirō and Kōji, and one younger brother, Yūya. He also has two sisters-in-law and a niece from his second brother's marriage and a nephew from his first brother's marriage. His given name comes from a character from the manga, Touch, written by a Japanese manga artist, Mitsuru Adachi. Coincidentally, bandmate Tatsuya Ueda was also named after the twin brother of Kamenashi's namesake.