Only 60 Minutes, Yet It Perfectly Captures the Starry Sky and Regret: Dream of Stars

This one is really short, you can finish it in under 60 minutes, so no need to commit to a long series. It's not the kind of heartbreaking story that involves loud shouting; it's quiet and slow, building up emotions that you can only truly feel by savoring it. The world-building is simple, focusing on the interactions between characters. The soundtrack is a definite plus. If you're looking for a short anime, don't want to binge a long series, and like a combination of 'end of the world' + 'gentle' themes, this is for you.