Enables serine-type endopeptidase inhibitor activity. Acts upstream of or within several processes, including T cell mediated cytotoxicity; acute inflammatory response to antigenic stimulus; and negative regulation of T cell apoptotic process. Located in cytoplasm. Is expressed in heart; lung; metanephros; and spleen. Orthologous to human SERPINB9 (serpin family B member 9). [provided by Alliance of Genome Resources, Apr 2022]