I for one welcome our new isekai'd overlord.
@
depzdai
The double-edged sword part was a liberty taken on the side of the translator I assume.
The original is more along the lines of "Cruelty is a [family jewels of a treasured groin sword] - Cruelty is a sword that can cut anything, but if you become obsessed with it, sooner or later this sword will become your undoing. / if you become dependend on it, it will spell your demise and/or destruction sooner or later.
Basically, the original said nothing about the sword being metaphorically double-edged and this is just a funny side effect of a good or bad translation, depending on the exact amount of you caring (measured in milligrams). Also, I suck at Japanese.