Definitely. 'Darkest Hour' aims to depict the truth of that era, but as with most films based on history, there could be minor fictional elements added to make the story more engaging and accessible to the audience.
It depends on your perspective. Berserk is definitely dark, with its violent and tragic storylines. But some might argue there are other mangas that could be equally or even darker based on personal preferences.
The story could center around a parallel Pokémon universe that has been overrun by a dark energy. This energy has warped the Pokémon and their relationships with humans. Trainers are no longer friends with their Pokémon but rather slaves to them. The main character might start as an ordinary trainer who discovers this dark truth and decides to fight against it. They have to battle against powerful, corrupted Pokémon and the dark forces controlling them, while also trying to find a way to free the Pokémon from this dark influence and return the world to its normal state.
The darkest part could be when the protagonist has to make an impossible choice that leads to tragic consequences, showing the depth of human suffering and moral ambiguity within the story.