Also, the fire absorption is Gen's power and not the switches...so is he not human?
He's human, but I think he can bring out the maximum potential of the switches.
My Theories:
With accepting J.K., he had to accept that he'll get bit back now and then (which explains the feedback from the elec switch), once Gen fully accpeted J.K., the feedback enveloped him and become the gold suit.
With wanting to accept Nozama, he had to accept everything she takes on a regular basis (as a goth) and so this is demonstrated as absorbing harmful flame. (as fire is uncontrollabe/temperamental)