There is a negative thinspace \! which is a negative version of \,.
Is there a negative version of normal character space \ too?
I could not find it in: Lengths and when to use them, What commands are there for horizontal spacing?, https://mylatexnotes.wordpress.com/2017/05/09/text-negative-white-spaces/

\could shrink/expand with the text, so it's not fixed. – Werner Dec 19 '19 at 15:42\fontdimen2but as Werner said that can shrink or stretch (\fontdimen3and\fontdimen4) so the space isn't really fixed. Are you by any chance looking for something like\unskip? – campa Dec 19 '19 at 15:46