Due to the fact by now there's somewhere between 12 batman comics and 650 billion batman comics I'm assuming at least once by now he has done that, or something to that effect
Pretty sure it's because in Gotham it's cold as fuck, especially in the night, so his breath also does the steam thing, only more badass looking cause he's Batman.
I mean I LOVE steampunk but I also LOVE Danny Phantom and dragons
And of course Batman
never seen AoT tho