Kashiwa, Chiba
Born in Kashiwa, Chiba, Japan, Sakai was introduced to football by his two older brothers and joined a school football team when he was the third grade of elementary school. He initially played as a striker before converting to a full back, a position he played today. Sakai spent 10 years with the school football team before joining Kashiwa Reysol U15 side in 2003.