Does steady breath and Vengeful fighter stack?

they dont stack. For Robin tho, i'd recommend warding breath instead.

Vengeful fighter is an amazing B skill but if you really wanna run one of those breath skills, then swap your b skill for vantage and give him the QR seal

If your asking if the charge will decrease by 4 when attacked, the answer is no. IS won't be doing that kind of powercreep for a few more months.

NO. IT SAYS SO ON VENGEFUL FIGHTER ITSELF.

And again, with Expiration AND Vengeful fighter
Close/Distant Defense is a much better option because the Breath skills don't stack with the fighter skills! Also 41 Def and 33 Res when being attacked is too good to pass up on!

Not going to stack but you can mix CD reduction skills that activate on different phases. You can do Heavy Blade seal with Venge for example.

Having steady breath and vengeful fighter would allow you to activate aether every time you are attacked, as long as they double you and you are above 50hp. Steady breath adds charge when attacked and when counter attacking, vengeful fighter only adds when counter attacking (but comes with the advantage of giving you a counterattack).
Edit: Forget mention, yes I know they don't stack but I'll show the maths as proof-
Steady breath and vengeful fighter: they attack, so you're 3 charges away, you attack so you're 1 charge away, they attack so aether is ready (there is an excess charge) and finally you proc aether on your final counter attack