Most people fail to understand the horrors of "nothing". It literally means "no thing", there is a lack of thing. Something is whole when all of it is full. Nothing is whole when everything except the absence is full. Nothing refers to something existing once, somewhere, and not there where you look. "Nothing is in my pocket" refers to the idea that there may be something in your pocket, but in reality, there's a lack of something.
There's where the horrors come in. Take, for example, a room. Say, it used to be the bedroom of a loved one. Then, something happens to that loved one and they are forced to get rid of the things in the room. I don't necessarily mean death, just, something happens. Then you would say that the room is full of nothing. Nothing is in that room. Nothing creeps in when tragedy strikes.
Or, maybe you can see an empty room as hopeful. When you move into a new place, the rooms are full of nothing, but they are expected to have future things in them. But, at the same time, the new place comes with a lot of new struggles and fears. Fear of the costs of moving. Fear of not having any friends. Fear of missing out at stuff back at home and getting homesick. And anxiety might creep in with the new nothing.
Nothing is akin to death. Your body becomes nothing when it dies. But you are no stranger to death yourself. After all, you're a ghost. So, at one point you were nothing. You had no form, you had nothing to do. Perhaps that's what is so scary about nothing to you. You were at one point nothing, and you don't remember that, but you fear that it may go back to nothing.
That's also what you don't get about Suki's fear of death. She has told you many a time, that she fears death more than anything. She knows that you are already dead. She also knows about the chef. So, she should be expected to understand that death isn't the end-all-be-all she thinks it is. Still, she worries avout death way too frequently.
The alchemiter, much like imagination in magic, is very useless as it turns out, removing the entirety of the machine.