Serine protease inhibitor that inhibits plasmin (IC(50)=43.53 nM, Ki=3.6 nM). Acts as an antifibrinolytic agent. May act in a cooperative manner with the serine protease Bi-VSP (AC B5U2W0) to promote the spread of bee venom under anti-bleeding conditions. Expressed by the venom gland. Does not inhibit factor Xa, thrombin, and tissue plasminogen activator (t-PA). Belongs to the venom Kunitz-type family.