This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / The Severing Crime Edge
Pretty much all of the killing goods.
Injection of Coma Death. A giant fucking syringe.
The Rulebook of Sentencing and Execution. The book is capable of summoning a noose... THAT APPEARS OUT OF THIN AIR TO STRANGLE YOU TO DEATH.
The Pet Whip of Submissive Butchery. A whip that can strip men of their free wills... It practically turns them into zombies.
Partly Nightmare Fuel and partly Tear Jerker: Iwai cradling the Crime Edge during the Night of the Living Mooks. There is something deeply unnerving about a fragile little girl lovingly hold into a weapon that is enchanted to kill her, given half a chance.