I’m thinking of something like the dark swan arc in once upon a time if it was done well if Emma had actually turned into the dark swan and her family had to save her.

Or characters making an impossible choice that costs them there soul

Also side note I’d love for the ending to be good but I love the angst and struggle along the way NOT looking for grim dark!!! More of a fan of more angst filled stories if that makes sense.

Or character becoming something they hate: Like Buffy in Buffy the vampire slayer becoming a vampire for example

Would love a female main character

Bonus if it’s sapphic or lesbian doesn’t have to be. ) but would love

Example dark magic starts taking ahold.

Or making impossible choices that corrupt them think of Anakin using the dark side in Star Wars and what happens. But I’d love a story where the Anakin character could be saved.