I know I'm getting some hate for this one!
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Ventus.
Okay, Ventus is seriously disliked by people, which I honestly DON'T understand, seeing as how popular similar characters like Roxas are.
Granted, Ventus has nowhere near the character depth as Roxas, but that doesn't mean he's not an awesome character.
Ventus' role in the series definitely seems to take the one of the younger, more immature kid, throwing tantrums, not thinking realistically, etc.
While Ven is a little immature, we also see him in some of the BEST moments of the entire game of BBS; when Terra is about to fight Master Eraques, when Vanitas is revealed, etc.
Ventus is not an amazing character by any means, but moreso than other characters of this series, he is truly an underdog I always find myself cheering for, and seems to fit this role more than most other characters.
And the entire impact Ventus has on Sora/Roxas' relationship is also too much of a reason for me to not include him.
I also find him just a bit less annoying than Kairi LOL
Hint for #8! - The ONLY true villain to place on this list! :)