The nucleocapsid (NP) protein of Severe Fever with Thrombocytopenia Syndrome virus (SFTSV) is encoded by the S segment of its tripartite RNA genome. NP plays a central role in viral replication by encapsidating the genomic RNA and forming ribonucleoprotein complexes with the polymerase. It is highly conserved among SFTSV strains and strongly immunogenic, making it a major target for diagnostic assays and serological studies. Because of its abundance and stability, recombinant NP is widely used as an antigen for ELISA, rapid tests, and antibody development against this emerging tick-borne phlebovirus.