Histone H3-like variant which exclusively replaces conventional H3 in the nucleosome core of centromeric chromatin at the inner plate of the kinetochore (PubMed:10524621). Required for recruitment and assembly of kinetochore proteins, mitotic progression and chromosome segregation (PubMed:11402065, PubMed:14522947, PubMed:16273096, PubMed:16950114, PubMed:16950115, PubMed:12080088, PubMed:15767665). May serve as an epigenetic mark that propagates centromere identity through replication and cell division (By similarity). Might promote cleavage furrow stability during cytokinesis (PubMed:23684975). Not required for chromosome segregation during meiosis (PubMed:16273096). Forms a nucleosome-like histone octamer containing two molecules each of H2A, H2B, hcp-3 and H4 assembled in one hcp-3-H4 heterotetramer and two H2A-H2B heterodimers. The hcp-3-H4 heterotetramer is more compact and structurally more rigid than corresponding H3-H4 heterotetramers (By similarity). Interacts with knl-2 (PubMed:17339379). Interacts with lin-53 (PubMed:26904949). Requires knl-2 and lin-53 for chromatin localization (PubMed:17339379, PubMed:26904949). Co-localizes with hcp-6 at prophase, metaphase, and anaphase chromosomes (PubMed:12080088, PubMed:15767665). Present at higher lower (>95%) level than cpar-1 (at protein level). RNAi-mediated knockdown impacts chromosome segregation leading to abnormal chromatin distribution (PubMed:16950114, PubMed:17339379). Disrupts mel-28 localization to kinetochores (PubMed:16950115). Leads to cleavage furrow regression and failed cytokinesis during the second embryonic division (PubMed:23684975). RNAi-mediated knockdown abolishes the localization of hcp-6 at the centromeres of mitotic chromosomes (PubMed:12080088). Belongs to the histone H3 family.