"The Hephaestus falling into the stage" is now making me think... theater AU where the climactic scene involves the lighting rig/main source falling on and almost killing Eiffel, Phantom of the Opera style

I'm glad my typos are a source of inspiration for you anon! It would be funny if Eiffel had the same frequency of near-death experiences as he does in canon whilst working in a theoretically less-hazardous environment like the theatre.