Sugiuchi went on to enroll at Kagoshima Jitsugyo High School, playing in the National High School Baseball Invitational Tournament and National High School Baseball Championship (the two most prominent national tournaments in Japan, both held at Koshien Stadium) a total of three times. In the summer of 1998, then-senior Sugiuchi matched up with Sendai Senior High School ace Hiroshi Kisanuki (currently with the Yomiuri Giants), a highly touted draft prospect, in the finals of the Kagoshima Tournament, defeating the school 3–1 and earning a berth in the national championship.