The firefighting game I played was building based, and a lot of it was trying to cleverly break through fire to get to water refills and machines that helped deal with the fire (sprinklers and gas mains mostly, or the keys to unlock them). There was also dealing with the fire spreading and the various ways it could do that (I thought flaming debris falling from the ceiling repeatedly was fun).

Naturally, a mecha game requires us to scale up a bit to deliver on the promise of being a big stompy mech. We could scale up the building - have the mecha in some kind of alien superstructure, maybe - or we could scale up the conflict from a single building to an entire city.

If we go with a city, there's lots of interesting things to play with. Water mains (and water main breaks!), electrical fires, gas mains, parks vs buildings vs roads, maybe lakes or ponds? I could see you piloting a kind of firetruck transformer which you can put out fires with, but your primary goal is to get the city's infrastructure repaired so that the city itself can help you put the fire out! Maybe you can rescue other fire teams or EMTs to help you out, too.

The game could vary a lot depending on how big you are, but I like this idea!