Interim Champion is a temporary title given to a boxer who is a replacement for a champion who cannot defend because of medical or legal purposes. The top two seeds fight to become the Interim Champion upon the reigning champion's suspension. When the real champion is capable of fighting again, he and the Interim must hold a title unification match to determine the official holder of the title.
Randy Boy Junior is currently the only Interim Champion to have appeared throughout the series, having acquired the OPBF belt from Miyata Ichirou following his medical leave. The case of Takeshi Sendou vs Alexander Volg Zangief was for the official title following Date Eiji's retirement, not an Interim one.