The story is after the first season, but before the second. Can be watched after the 23rd (before last) or after the 24th (last) episode of the first season as the story is technically a continuation of a part in the 23rd episode. This is a very short story put into two episodes in which Rimuru makes the golem he promised to Ramiris after destroying her guardian golem. If you wish to see what exactly Rimuru does and how the golem is created (as it wasn't really explained in the main story) then take a look and see for yourself. The art style is the same as the original,so are the animations and voice actors.
Characters do not feel out of place nor do they do things which they normally wouldn't do.

In my opinion, this story is more for those who wish to see more of "Slime Anime" than for those who are just here to watch the main story and move on.