The Music Box Girl by K.A. Stewart
The gender-swapped steampunk Phantom of the Opera that you never knew you wanted! Stewart's story takes place in a shiny alt-history Detroit, complete with steam-powered robot servitors, mechanical glories and, of course, airships.
The Music Box Girl follows three point of view characters. Tony is our Christine - he's a young man from a (hand-wavey) other country, here to make his destiny as a singer. He gets a job as a stagehand at the prestigious Detroit Opera House, but his after hours crooning earns the attention of the Opera House's very own phantom. Bess is Raoul. She's also from (wherever) and is a childhood friend of Tony. But whilst Tony is carving out a living as a prop-duster, Bess is an international tomb raider. Tired of society and its conventions, she carries guns and buckles swashes and dashes and dives in and out of adventures. But, secretly, she might be craving something a little more... romantic.