Iinuma is a dumbass, most of the girls he knows are straight up monsters, he should know better; idk he has no reason to think girls are weak and therefore it's unmanly to fight them
Only one person is needed to solve every problems; however, she is currently taking her bath. Just take your time Ranna, no one is dying in this manga anyway.
@pokefairy
Well, it doesn't have to be that he reasons "girls => weak => fighting them unmanly", just "girls => fighting them unmanly". She'll wipe the floor with him, he'll still have qualms about fighting her.