This study proposes the multiple reconfigurable intelligent surface (RIS) based index modulation (IM) called as MRB-IM, in order to improve the channel capacity by activating one or more RISs among multiple RIS (MRIS) and utilizing its number of combinations. The ergodic capacity analysis is derived to prove the validity of the simulation for the Rayleigh fading channel. Generally, MRIS suffers from inter-RIS interference (IRI) which is considered as the leverage of the secondary reflection amongst the MRIS. Despite having a larger capacity, the proposed MRB-IM has less of an impact on IRI because occurs among active MRIS. Simulation results demonstrate that the proposed system outperforms the existing MRIS in terms of capacity with and without IRI. In addition, bit error rates with different activation numbers of elements and RISs are shown. Here, the maximum likelihood on the receiver side is adopted to estimate the selected RIS index and information symbols in this study.