Recently an induction heating system comprising a pair of no-insulation high-temperature superconductor (HTS) racetrack coils was built and now it is commercially available. It generates a direct current (dc) magnetic field in which a conductive metallic billet rotates at a high speed. Most dc induction machines accommodate a "single" billet per operation. This paper proposes an alternative concept of a "multiple-billet" induction heater, where the multiple billets can be simultaneously heated. The system consists of eight pairs of HTS racetrack coils that are placed in a circular pattern. An arbitrary number of billets may be placed and rotate at the same time in the space between racetrack coil pairs. The main goal in this paper is to theoretically demonstrate the principle of operation of the new multibillet system. The paper presents: first, overall system configuration and the principle of operation; second, electromagnetic design of the eight-pole HTS magnet; third, analyses with key operation parameters to estimate the multibillet heater performance. Due to the "positive" mutual inductance among neighbor racetrack coils, the multibillet system is estimated to deliver a larger heating power per billet than that of its single-billet counterpart for given operating conditions. Also, due to the eddy-currents induced in each billet, the power per billet reduces when the number of billets increases beyond an optimal value.