[hildea]

Hm, a very good question, but not so easy to answer. Some suggestions:

Lies of Locke Lamora by Scott Lynch. A gang of young swindlers take on a powerful mafia organization. It's darker than Onepiece, as the main motivation is revenge, but the Gentlemen Bastards feel a lot like the Straw Hat Pirates (including being incredibly competent at what they do).

In Other Lands by Sarah Rees Brennan. A portal fantasy where a kid from our world is invited to a school in the magical Borderlands.

Elliot had “does not interact well with peers” on all his report cards. If the teachers had been more precise, what they would have said was “does not shut up well around stupid people,” but that was teachers for you.

Both fighting for what you believe in and following your dreams are major themes. It's also one of the few books which has both made me laugh out loud and tear up.

Sorcerer to the Crown by Zen Cho. It has less of the feeling of freedom/we can do anything we want: The protagonists are dealing with serious threats which they can't ignore. But the other themes you mentioned are there. It also contains my favourite paragraph ever:

Prunella had once thought life in London would be all flirting and balls and dresses, hitting attentive suitors on the shoulder with a fan, and breakfasting late upon bowls of chocolate. She sighed now for her naïveté. Little had she known life in London was in fact all hexes and murder and thaumaturgical politics, and she would always be rising early for some reason or other!

I hope you get more suggestions, I'd like to read more books like this too!

I've seen some people writing about the genre hopepunk, as the opposite of grimdark. You might find some promising books searching for that.

So the essence of grimdark is that everyone’s inherently sort of a bad person and does bad things, and that’s awful and disheartening and cynical. It’s looking at human nature and going, “The glass is half empty.”

Hopepunk says, “No, I don’t accept that. Go fuck yourself: The glass is half-full.” YEAH, we’re all a messy mix of good and bad, flaws and virtues. We’ve all been mean and petty and cruel, but (and here’s the important part) we’ve also been soft and forgiving and KIND. Hopepunk says that kindness and softness doesn’t equal weakness, and that in this world of brutal cynicism and nihilism, being kind is a political act. An act of rebellion.

(Alexandra Rowland)