Shirota was born on December 26, 1985 to a Japanese father (城田光男) and a Spanish mother. Shirota lived in Barcelona, Spain from when he was three to about seven years. He returned to Japan for elementary school and can still speak Spanish in ordinary conversation. He attended high school at Horikoshi High along with NEWS member Yamashita Tomohisa, WaT's Teppei Koike, Japanese actor Ikuta Toma and KAT-TUN's Akanishi Jin and Tanaka Koki. According to Shirota, when he was little, his family liked to sing songs, so he would borrow his older sister's keyboard, while his mother taught him piano. Thus spawned Shirota's love for composing. He composed his first piece when he was in the fourth grade, titled "The Tear".