The Darkest Minds is considered science fiction for several reasons. It has a fictional world with scientific concepts at play, like genetic mutations giving people special powers. Plus, the story often involves themes of scientific exploration and the consequences of technological progress gone wrong.
One idea could be a crossover with The Hunger Games. The characters from Darkest Minds could be thrust into the arena, and their special abilities would give a new twist to the survival challenges. For example, Ruby's power to control minds could be used to manipulate other tributes or even the Capitol's forces.
Create a strong plot. Maybe there's a common threat that forces the characters from both universes to work together. Or perhaps there's a mystery that only their combined skills can solve. For instance, a powerful dark force is spreading across both worlds, and the heroes must find a way to stop it. Make sure the plot moves at a good pace and keeps the reader engaged.
You can try looking on fanfiction websites like Archive of Our Own (AO3). There are likely numerous stories there that feature Ruby and Liam sharing a kiss. Just search for 'The Darkest Minds Ruby and Liam kiss' in the search bar, and you'll be presented with a variety of options written by different fans.
The chemistry between Ruby and Liam in the original story is part of it. Fans love to see that relationship explored further in fanfiction, especially with a kiss which is a very intimate moment. It allows fans to see their favorite characters in a more romantic light.
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.
Don't forget about fan - fiction websites. While they are mainly based on existing fictional universes, there are often some really good adventure stories with dark twists. For instance, in the Harry Potter fan - fiction realm, there might be stories that take the characters on a much darker adventure than in the original books.