Webgenya joins the fight by pulling out a gun and using it to blow the heads off of the various hantengus that start to pop up when the demon is beheaded.
It's yet to be.
Webbut it is revealed in episode 6 of season 3 (chapter 115 in the manga) that genya is, in fact, incapable of performing any breathing techniques.
Webthe strongest hashira of the demon slayer corps, gyomei himejima, personally trains genya to help him compensate for his inability to use breathing.