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Composite quantum compounds (CQCs) have become an important avenue for the investigation of intercorrelation between two apparently different fields of physics. Topological superconductors, axion insulators are few such CQCs which are recently drawing tremendous attention in the community. Topological nontriviality and Rashba spin physics are seemingly two incompatible quantum phenomena but can be intertwined within a CQC platform. We have presented a general symmetry based mechanism, supported by ab-initio calculations to achieve intertwined giant Rashba splitting and topological nontrivial states simultaneously in a single crystalline system. We have achieved Rashba splitting energy and Rashba coefficient values as large as 161 meV and 4.87 eV Å respectively along with Weyl semimetal phase in KSnSb_0.625Bi_0.375. These values are even larger than the values reported for widely studied topologically trivial Rashba semiconductor BiTeI. The beauty of our systematically analysis is that one can achieve various topological phase without compromising the Rashba parameters, in this CQC platform.