It’s safe to say that the role of conflict in stories has been covered already.
I’m the same in that I was (still am, sometimes) really wary of incorporating darker themes into scenarios, because I emotionally invest a lot into my charcaters. I really wanted to explore violence and conflict, but I didn’t want to “taint” the characters I was using and also, it had to make sense (talking about romances in particular, but can also extend to friendships or other relationships). I like nice, healthy relationships so it was difficult to imagine, for example, the main giant as a sadistic abuser AND for the story to have a nice fluffy ending for the main giant and tiny. For example, some romances don’t make sense to me, or are not something I would call “romantic”. Like, the “I can fix him” trope is not something I usually subscribe to. Also, Ross and Rachael (iykyk).
In line with @Mrgoblinging7, I create “throwaways” - one-shot, stand-alone and non-canonical scenarios that focus on the dark stuff. I can incorporate regular characters, or make new ones entirely, it doesn’t matter. The scenario is only on whatever theme(s) I’d like to explore - I don’t worry about how it fits in with a fluffy scenario. Not yet. It’s about getting comfortable and understanding what I’d like to see; what would work, what wouldn’t if I did try to make it canon.
If that kind of dynamic between the main characters doesn’t work, but I still want someone to do something, then I use other characters to fill darker roles. Sometimes that’s a matter of preference though - you might not like having another character involved in the dynamic.
Sometimes it’s about reframing the story entirely - would I call something a romance? Or is it better described as a drama, tragedy, horror, etc.? You can have nice elements in all of these, but they’re secondary to the overall theme. It might start off nice then devolve into something darker. Maybe it’s always been fucked up, but it’s never been realised until a point.
Anyway. Those are my thoughts and approaches 