Animal sidekicks have been dogging heels for decades, some beloved and some best left forgotten. Animal -- or at least animalistic -- sidekicks have the power to become the very face of an anime, or else become so universally hated that they go down in infamy. What is it that endears an animal sidekick to an audience, and what makes it so that they can't get off the screen fast enough?
First and foremost, animal sidekicks need to have a strong visual element. Pikachu from Pokémon, Jiji from Kiki's Delivery Service and Luna from Sailor Moon all have something in common -- they're incredibly cute. The best animal sidekicks are fun to look at, and not only because they're cute but also visually distinct. For instance, compare Pikachu with Myoga from Inuyasha. Myoga is a tiny, ugly flea with no distinguishing features. He causes itchiness merely by appearing on screen. Pen Pen from Neon Genesis Evangelion also commits the crime of being not particularly cute. He is a normal penguin who appears at random times and doesn't seem to have a purpose other than being a penguin, so it's easy to forget his existence entirely.
Aside from being cute and having a distinct appearance, purpose is also important in determining whether an animal sidekick will be successful. While Myoga at least delivers information, Pen Pen is simply there. The story of Inuyasha would change a little if Myoga didn't exist, but Pen Pen is inconsequential to the plot. Being an ordinary and rather ugly penguin who adds absolutely nothing to the storyline makes Pen Pen an ineffectual sidekick, while Myoga surpasses him (albeit only just) by at least being useful.
Of course, plenty of beloved animal sidekicks don't have much purpose. Ao from Yona of the Dawn and Xiao-Mei from Fullmetal Alchemist: Brotherhood are adorable animal sidekicks who don't contribute anything of note to the story. Ao is cute and Xiao-Mei at least matters a little to the plot as the 'lost cat,' but if a sidekick is going to exist in the first place, giving them a real purpose for being there is an economic use of character, as well as making their potential loss all the more meaningful.
Kirara, also from Inuyasha, is an example of a sidekick with real purpose. Kirara is both adorable and visually unique, and acts as Sango's mount in battle. She also brings out the soft side in the battle-weary Sango. Kirara is also constantly useful throughout the series both in battle and for Sango's character, making her a much better sidekick than a straight-up cute one. Sadaharu from Gintama fills a very similar role in being useful during conflict on top of being cute and visually distinct. It's having a solid purpose that sets these sidekicks up for real success.
However, it's a careful balancing act to make sure an animal sidekick has a purpose without giving them too much of a role. Multiple episodes dedicated to a sidekick are a sign that the creators might be giving up on their main characters. If a sidekick eclipses the main characters, they've failed as a sidekick because they aren't technically one anymore. For example, Elizabeth, the unknown species of sidekick from Gintama, ends up having an entire arc dedicated to it. This ultimately works due to Gintama's gag nature, but would have spelled almost certain doom in just about any other show.
Although the amount of purpose a sidekick can have needs to be carefully considered, this doesn't mean they always have to sit on the sidelines. Animal sidekicks can take their purpose up a notch in a way that doesn't overshadow the main characters, yet still reveals hidden potential. The penguin trio from Mawaru Penguindrum is an example of this done (nearly) right. Mawaru Penguindrum is full of symbolism, and the adorable penguin helpers serve to either prod the story along or aid with that symbolism. They are adorable, recognizable and serve a purpose -- although Mawaru Penguindrum is so full of symbolism that the penguins get lost in it, making their role as aids to the story confusing at best.
However, animal sidekicks can without a doubt be successful supports to a story by becoming more than what they seem. For example, Cerberus from Cardcaptor Sakura has a far larger significance than his initial teddy bear appearance suggests.
Kyubey from Puella Magi Madoka Magica is one of the most infamous animal sidekicks for this same reason. While part of what makes a successful sidekick is fulfilling a purpose, Kyubey goes above and beyond in becoming an antagonistic force within the story. He is not only cute and visually distinct, but also has a secondary purpose to make him interesting. Kyubey differs from other sidekicks here in that he does control the balance of the story, but while this normally wouldn't be a good thing in a sidekick, the story remains focused on the girls. Since Kyubey does not transform into some kind of evil final boss, his role as an antagonist animal sidekick works very well.
However, one important thing that sidekicks are capable of doing that makes them top tier is complement the main characters by bringing something out in them. Kyubey does bring out something new in Madoka, but sidekicks with a positive influence have more potential for long-lasting relationships. For this reason, Nyanko-sensei from Natsume's Book of Friends is a top-tier animal sidekick who ticks every single box. He is cute as well as visually distinct. He has a constant purpose in the narrative. Although he transforms into his enormous Madara form to end certain physical conflicts in the show, the story remains focused on Natsume's emotional journey and development, meaning that Nyanko-sensei doesn't threaten to unbalance the narrative.
Instead, he offers exactly what the story needs at the time, whether this is humor when Natsume is accidentally turned into a young child or tactful silence when Natsume finds his empty childhood home. He's also a loyal companion -- no matter how often he claims it's just so he can eat Natsume later -- and his relationship with Natsume is utterly charming. Moreover, he brings newfound confidence out in Natsume as his friend and protector, and is the one to kickstart Natsume's attempt to return the names in the Book of Friends.
So, what makes a successful animal sidekick? First, it helps if they're cute. Being visually distinct as well as appealing can help secure their place in the show. Besides appearance, having a purpose within the story without overshadowing the protagonists helps endear a sidekick to the audience and make their loss more potentially devastating. Sidekicks can sometimes flip their roles around or aid with symbolism, although this needs to be done with care in order to be effective. Finally, the best sort of animal sidekick is one who brings something out in the protagonist, complementing their development and overall story. While any animal sidekick can be worthy of love, only those who meet these expectations truly become irreplaceable parts of their respective stories.
