Not all Quirks in My Hero Academia are created equally, and Fumikage Tokoyami from Class 1-A might have one of the most unusual in his class. Tokoyami's Quirk, Dark Shadow, is sentient darkness that sprouts from Tokoyami's body, obeying his commands in the heat of battle. It might be easy to confuse Dark Shadow as just an extension of Tokoyami's will, but Dark Shadow possesses an intent of its own. Under certain circumstances, it can even overpower Tokoyami, as seen during the Forest Training Camp arc.
In fact, the way that Tokoyami commands Dark Shadow is remarkably similar to how Pokémon trainers command their own captured Pocket Monsters. While Dark Shadow isn't a Pokémon (Dark Shadow can say far more than its own name), Tokoyami's relationship with Dark Shadow is remarkably similar to that of monster and master, with Dark Shadow being a sentient entity that needs to be commanded by its 'trainer,' Tokoyami.
To explain in more detail how Tokoyami's Dark Shadow is like a Pokémon, we first need to go over how Pokémon trainers fight with their monsters. Pokémon harness elemental powers that they can channel into combat and fighting, based on the commands of their trainers. This is, again, much like how Tokoyami commands Dark Shadow to attack. Dark Shadow, as its name indicates, channels the power of darkness.
However, more important than that, Pokémon have resistances and weaknesses. Environmental factors can empower Pokémon. The move Rain Dance, for instance, allows Water Pokémon to gain greater water power when fighting. Similarly, when surrounded by darkness, Dark Shadow's power increases greatly. The darker it is, the better it is.
However, once again, as is the case with Pokémon, when confronted with his weakness -- light -- Dark Shadow is weakened. Bakugo, for instance, can use his flashing light and fire to drastically weaken Dark Shadow. Again, this is much like what happens with Pokémon. Fire Pokémon are incredibly weak against Water Pokémon. Even Dark Shadow shrinking under a blaze of light has a direct parallel in Pokémon lore. When the flame on Charmander's tail is snuffed out, Charmander dies. The wetter it gets, the smaller the flame becomes.
The final comparison between Tokoyami's Dark Shadow and Pokémon that establishes the two as remarkably similar is the manner through which Dark Shadow, if too powerful, refuses to obey Tokoyami's commands. In Pokémon, Pocket Monsters have levels. If a Pokémon levels-up too much, then they might become too powerful for a trainer to command. The only way to control a Pokémon is to gain Gym Badges, which are physical proof of Pokémon mastery.
The comparison between Tokoyami and Pokémon trainers can be viewed as just a fun compare-and-contrast between two iconic anime. However, on closer inspection, it actually feeds into the character creation of My Hero Academia. My Hero Academia is both a compelling and unique story in its own right and a tribute to the superhero media that we have grown to love over the years. Obviously, characters like All Might are tributes to heroes like Captain America and Superman -- paradigms of justice.
By this thread, Tokoyami could be thought of as an accidental tribute to the heroes kids during the '90s grew up with: Pokémon trainers. Ash Ketchum, for multiple generations of kids, is an iconic protagonist, and Pokémon allowed kids to project themselves onto him and other trainers. Ash was (and still is) a relatable kid fighting alongside cool monsters and embarking on fantastic adventures. Tokoyami is sort of an edgy reflection of that. In a sense, Tokoyami is what teens who grew up wanting to be Ash Ketchum probably wish they were -- Pokémon's rules, just with a blacker coat of paint.