Natural killer (NK) cells mediate antibody-dependent cellular cytotoxicity (ADCC) by binding antibody-coated target cells via their Fc receptors. In our previous study, we demonstrated that 25KDa branched polyethylenimine (25KbPEI) enhances the antitumor activity of NK cells, referring to them as Chem_NK. Building on the mechanism by which 25KbPEI primes NK cell function, we propose its potential for clinical application to CD38-expressing multiple myeloma. We discovered that 25KbPEI induces endocytosis of CD38, a protein highly expressed on the plasma membrane of NK cells. Internalized CD38 produces ADPR, which acts as an agonist for TRPM2 calcium channels localized on lysosomes. This triggers intracellular Ca²⁺ mobilization, leading to increased cytosolic Ca²⁺ levels. Elevated cytosolic Ca²⁺ drives the convergence of lytic granules toward the microtubule-organizing center (MTOC), a process mediated by AMPK signaling activation. These findings identify CD38 internalization as a critical step in the chemical priming of NK cells. Utilizing this mechanism, we demonstrated that Chem_NK exhibit synergistic efficacy with daratumumab against CD38-expressing multiple myeloma, both in vitro and in vivo. We suggest that the internalization of CD38 in Chem_NK prevented daratumumab-induced fratricide of NK cells. These results highlight the potential of chemical priming to enhance ADCC efficacy and mitigate off-target effects, providing a promising strategy for NK cell-based therapies in multiple myeloma.