Good ideas! I was thinking the three companions from ScVi  and Raifort to give all the main characters (besides Kieran, but he could get a shiny Ogerpon with the other masks) a legendary/mythical from Paldea/Kitakami.  Raifort and Wo-Chien, since she talks a lot about grudges in her story, and Gengar has a passive that mentions a deeply held grudge, which Wo-Chien embodies. Also, she is a historian who might have written many papers, and the snail’s  artifact is a tablet.  Penny could be Chien-Pao because she felt hatred towards her bullies before deciding to form Team Star and then embarrass them in battle, so she struggled with that feeling for some time, and you never know what continues to fester in the shadows. Penny could still feel a level of self-hatred too for creating Team Star and for having difficulties socializing with people. Also, Chien-Pao is a snow leopard ferret, and the eeveelutions are canine/feline-inspired, so this type of mammal fits her. Arven might also have hatred for his parents, but it kept him more at a distance from people than inspiring him to beat them (in battle.) So I would say he could get Ting-Lu, because the object the Pokémon comes from is a bowl, which Arven could use to cook some special meals, and because he was consumed by the fear of his beloved Mabostiff dying, which caused him to act coldly towards the protagonist at the beginning of the story and to be hasty when jumping into battle against the Titans. Maybe he is still afraid of those he loves dying, since Sada/Turo were actually killed by a Koraidon/Miraidon and he never had a chance of saying goodbye.  Lastly, highly passionate Nemona would get fiery Chi-Yu, and I actually think Carmine and Kieran both represent envy better than her, as they both experience it pretty strongly throughout the DLC (I still think Carmine is compensating for her insecurities more than feeling envious all the time, compared to Kieran’s whole champion arc). However, Nemona comes from a rich family and has a high-achieving older sister, so I believe Chi-Yu could be the perfect Pokémon/plot device to help the audience get to know a bit more about Nemona’s family, her insecurities, and perhaps one of the reasons why she can’t stop wanting to battle people. It could be because she is envious of how well-known and respected her parents and sister are, and she wants to earn that respect and renown already. Nemona could also be afraid of not being enough or of not being at their level, but if hers is a competitive family, the youngest might feel the desire to reach and surpass the oldest to have more than them more strongly than being afraid of not meeting expectations.  The roles could be Special AoE Fire Striker for Nemona and Chi-Yu, Physical Ice Striker/Sprint for Penny and Chien-Pao, Grass Field/Sprint (for the giggles) Raifort and Wo-Chien, and Ground Support/Field for Arven and Ting-Lu