The preview for Re:Zero’s 25th and final episode was written by Akatsuki Natsume, the author of KonoSuba! Akatsuki Natsume and Nagatsuki Teppei (author of Re:Zero) are good friends, and she was allowed to write the script for the preview of two key episodes 18 and 25. Of course if you haven’t watched the series, the preview is a spoiler.
https://www.youtube.com/watch?v=e1lxY1EyrJo&feature=youtu.be