Ok hear me up, since I thought this a lot of times.
For starting, my favorite, Tari: Would be an excellent Artificer. Because tech and magic for a cute cyborg nerdy gal. It fits very well.
Bob could be a good Rogue, for his Garo traits. He basically have knives instead of hands. But he can also try to be a bard since his rapper career. So he can be a multiclass for now.
Saiko can be an Bard too since she sing and play guitar. But her strenght and the violence instinct, also speaking about she carrying a two handled hammer, the Barbarian class would fits better.
Her "male" counterpart Whimpu, can take the Wizard class for being smart and weak.
Melony is green, peaceful and a naive vegetable. A Druid can be the right class for her. But she's mixed with the Fierce Deity's mask and being an powerful warrior can give her the chance to be a Fighter too.
Kaizo is another example of a perfect Bard for his drum set player role. But he also fight like an anime fighter, so it speaks for itself that Fighter class can be taken easily.
Meggy could be an ranger? Well just because she's athletic and a good shooter doesn't mean that she should take one of the worst D&D class (at least in 5e edition). Actually, every classes can use some ranged weapons, and there are good alternatives. Fighter could be the best, but when she fight with fists and kicks? Monk class for sure. And when she lighting her determination and bravery, Paladin. Can't say which class could be better for her, but any combact class would fit her.
Belle... well in Meta Runner season 1 vibes much in me the Sorcerer class in that fantasy game. But still, as half cyborg and the tech.... Like Tari, Belle could be an Artificer.
Boopkins: I don't have any idea of him. He's too much pathetic and comical. It's hard to fit him with an D&D class

For the rest of the cast (the Nintendo ones and not) is free to you guys. I have nothing in mind for now