Because this came out immediately before the main series, the characterization of Yokoi's relationship with Seki isn't very developed yet. In the first one, she doesn't get involved at all or drawn into any narrative. In the second one, she resists for far longer than she would, and gives in because cats are adorable. And cats are, indeed, adorable. To be honest, because of this, I would recommend watching this before the main series because it's a little jarring to come in expecting a sequel where they might get a little closer and find out that it's (from your perspective) a reset to the beginningof the show.