Destroy Me by Tahereh Mafi, #1.5 in Shatter Me series
I assume that Mafi wrote this novella to make the reader more sympathetic toward Warner, but it didn't work at all, at least for me. While it offered some more specific details about Warner's life and background, they all fit into the framework established in Shatter Me (which... good, in a way), so there wasn't anything that really made me like him better. And listening to his thoughts, in his own voice, about Juliette and about the civilians in his control made me less sympathetic to him, rather than more. As is the case in too many love triangles, he sees Juliette as a prize to be won rather than a person with agency, and he goes on and on about how painful her pain is to him. Um, probably pretty painful to her, too, dude. Way to make it all about you.
That said, it's always nice to get more information about a fictional world, and I'm still interested enough in general to read the next book. But this one made me firmly Team Anyone But Warner, and I think that was the opposite of the author's intention.