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New starters tend to have some sort of progression theme, either the Pokemon progresses further 'into' a theme, or does a 180 'out of' a theme. Gamefreak seems to have become fond of this. They didn't really start doing this until Unova and to a slightly lesser extent Sinnoh; before then it was mostly just 'it gets bigger with the theme downplayed' (that's not to say the other gens didn't do it, it was just far less pronounced). We can use this to predict based on the defining traits of the new starters where they will likely go.
Kalos' generation seems to be a 'lean into' theme one
>Chespin is a hedgehog which starts off light on the chestnut theme but then leans into it, with the chestnut essentially almost taking over the Pokemon
>Fennekin starts off as a broom, which it then leans into, which then becomes a witch as witches ride brooms
>Froakie's backpack evokes a thief, which then obviously becomes a ninja
Alola's generation is a '180 theme' one
>Rowlett has wide eyes and then slowly goes blind, a 180 from how owls are conceptualised, subverting expectations; by the time Decidueye comes along, it needs glasses
>Litten is lithe, as a kitten and gets a little burlier, but ultimately does a 180 becoming a heel wrestler instead of the way we would conceptualise a lithe cat
>Popplio, much to the dismay of /vp/ went similarly 180, going from the clownish seal to a primadonna mermaid again utterly subverting expectations
Galar's generation is another 'lean into the theme' generation, with arguably Inteleon not following the rules but even then:
>Sobble goes from neurotic and sad to quite calm and collected quite quickly, symbolising dealing with depression and growing up into a competent sniper, leaning into the theme
>Grookey and Scorbunny both lean into their themes quite well, with both of them starting off being drummers and soccer plays and then...just getting better at being soccer players and drummers