You're probably better off just getting a gadget or weapon for a death touch. Something that shocks someone with an overly lethal charge of electricity, or a sonic paralyzer. Or just poison.

Edit: This is is for some sort of hypothetical future Sapphire, her suped up semblance is a bit between "Master Illusionist" and "Reality Warper" depending on how powerful she can manipulate the senses. Even at the low end "Master Illusionist" you could completely numb them to pain (But not make them immune to death) with a false illusion fo you politely chatting with them from afar, while the real you slits their throat without them being none-the-wiser. Alternatively if she could use her power to say, convince them that they are being crushed by 50 tons of molten iron, their body may react accordingly, breaking it's own bones and gaining sever burns just because it thinks it's going through it. Again, extremely powerful stuff.

In Pathfinder the former is simply a trick of Greater Invisibility and Major Image, while the latter is more or less a Phantasmal Killer. I'd prefer the former, since even on the off chance that you can see through the illusions, you at least have the advantage of a semi-permanent invisibility.