Stop being dull, their is some degree of conductivity in everything even insulators.
That's why being conductive is a measure of how well a thing conducts electricity. Water for instance cannot pass electrons thus it does not conduct electricity well. Likewise, if you knew anything about conductivity as I stated at the outset, you'd find the slug is not conductive.
Furthermore, Raikiri blatantly is powerful yes, but it's no Kirin. If you want to pretend that a slug that can melt and divide and reform at will, telepathically communicate, and heal has the same biological properties as everyday slugs as we know them, then Katsuyu is not conductive as living organisms generally aren't conductors. Meaning that damage from raikiri dissipates as it leaves the Area of Impact. Sorry, you don't understand how conductivity works but that's it.