Pacifier

If End of Reason is the most terrible type of a superweapon, then Pacifier is certainly the least terrible one. Unlike all others it wasn't made to cause even a single death to anyone. Rather than that, it works completely differently... while still making the target stop being a problem forever. Or at least in a very long time period.
Pacifier is another type of spatial distortion weapon - like Reality Merger, Chaos, Spatial Distortion Generator or, probably, End of Reason. This time - a voidtech.
It works by phasing entire world or star system into some different dimension. Unlike End of Reason the disappearance isn't perfect, so from time to time nearby listening devices will pick up transmissions from the isolated system, which serve as a definite proof that whoever gets hit by this weapon actually doesn't die. In fact, they can still see the world outside of the distortion quite well.
What's more, it seems to simultaneously change any afflicted star into a Void Star (that have a beneficial effect on every living being that lives 'under them', improving their health etc.), while quickly terraforming any and all of 'devoured' planets into Paradise Planets. Because of that, there are at least several cases of worlds that were hit by the Pacifier simply because their inhabitants wanted it - or because that was the only chance of saving an inhabited world from some catastrophical terraforming failure etc. It is actually believed that Pacifier wasn't even created as a weapon but as some hyperadvanced species paradise assembly kit, but current Mankind simply lacks knowledge to enter or leave the afflicted area.