Rainbow Line, (Japanese: レインボーライン, foaled 1 April 2013) is a Japanese Thoroughbred racehorse and sire. He showed promise as a two-year-old in 2015 when he won two of his five starts. In the following year he recorded his first important victory in the Grade 3 Arlington Cup and went on to finish third in the NHK Mile Cup and second in the Kikuka Sho. He failed to win in 2017 but ran well in several major races. He reached his peak in the spring of 2018 when he won the Hanshin Daishoten and the spring edition of the Tenno Sho but sustained a career-ending injury in the latter race. He was a "hold-up" horse who was typically restrained at the rear of the field before unleashing a late run.