Checking some series, I'm surprised that as late as Bioman and the Kamen Rider ZX special, 1984, they still didn't have that (at least not consistently - they just slash grunts with no effects at all, but could use sparks for some specific stuff - like Apollogeist's slashing shield attack as early as X(1974)). Liveman(88) seems to be the first time where they use sparks universally, slash attacks on grunts or monsters. Black (87) also had sparks (or some powder?) used for almost every slash, but in this case it was mostly monster/villain attacks against the hero, so it's not quite the same as using sparks even to show hits on throw away grunts.
Maskman used sparks for monsters/climatic battles, but not when the heroes were just slashing grunts (or at least they do so very rarely), so I guess Liveman is the point where it became an universal effect.
