I don’t actually play SSBU and don’t know anything about the playstyle of each character, so this will just be based on the Aesthetics of each character instead. To prevent the list getting long and again, since I don’t know the game that well, I’ll limit it to a few major fankids.

Emery: Meta Knight (always plays with Gavin)
Gavin: Kirby (always plays with Emery)
Renato: Cloud
Tipha: Samus
Roy: Incineroar 
Draco: Corrin
Ulyssa: Snake
Sage: Pokémon Trainer
Celeste: Inkling
Levi: Bayonetta
Tanith: Isabelle
Maddie: Palutena
Aurélie: Little Mac
Primrose: Zelda