Serine protease which, in males, acts as a promoting signal during mating to activate sperm. In the male gonad, probably maintained inactive by swm-1. In males, partially colocalizes with swm-1 in vesicles near the apical membrane of cuboidal cells (PubMed:30470702, PubMed:22125495). During the spicule insertion stage of mating, secreted by the male vas deferens and transferred together with sperm into hermaphrodites where it spread into the uterus (PubMed:22125495). Specifically expressed in the male gonad including the seminal vesicle, the valve region and the vas deferens. Expressed in male L4 larvae and adults. Belongs to the peptidase S1 family.