Antique painblade
From Backstage Lore Wiki
The antique painblade is the traditional precursor to the modern day's Painblade. In ancient times, Jin-Mei soldiers riding to the field used to plunge their swords into filth, in the well-founded expectation that the wounds they inflicted would cause infection and rot. This nasty tactic was given new life when royal technicians (in those days referred to as Nuyin, something akin to "wizards") developed a blade whose surface, when unsheathed, swiftly attracted and encouraged bacterial growth, giving life to all kinds of deadly filth.