Pokemon: Pichu to Pikachu

Both nicely animated side adventures staring the animal companions of their respective shows. The the MCs are just cameos in the background while you get a glimpse of the crazy shenanigans they got up to when the human characters weren't there. I regularly think back on both of these for how plain fun and enjoyable they are. Not to mention both shorts were also made as tie-ins to watch with a feature length film.