I think it sounds fun to have a certain weapon stance when your breathing bar is in effect, this could just be a cosmetic option to really make your character yours
EXAMPLE: when ThunderExampleDude7594634 holds the breathing button, he goes into a Thunderclap stance or some shit which also changes his running animation to suit that stance. 
EXAMPLE: When RengokuDRider71483 holds breathing button, he goes into Rengoku Purgatory Stance, which also changes his movement to suit the stance
Could be bought with cash or robux or whatever the hell lol, maybe using these anims could put effects around your character in spurts or whatever. Maybe the effects could be a seperate gamepass, who knows!
That's all from me, peace 