Writing an arXiv paper without "Introduction" or "related work" sections
ArXiv's submission guidelines state that

Submissions to arXiv should be topical and refereeable scientific contributions that follow accepted standards of scholarly communication.

A manuscript that doesn't provide any context is unlikely to meet that standard, and may be declined by a moderator. In any case, the golden rule in technical communication is to consider the audience (hopefully your preprint will find some interested readers!) and what they'd find useful. Context and discussion of the relation to prior work tend to be quite useful.
Note, however, that ArXiv's guidelines don't specify that you need to write a perfect introduction. I've sometimes found myself stuck on one or two key opening sentences, trying to get them just right, instead of writing productively. If you face a similar issue, here's a method I've found useful. First consider what points you want to make, and maybe key works you want to cite, in order to have some structure to work from. Then force yourself to just put something down on (a possibly figurative) paper, in order to get started. If you edit that a few times, I would be surprised if you don't have something that's at least refereeable. More advice along these lines can be found here.