This guy's power is downright stupid if it is HIS imagination that comes true. then again there are various ways his powers could actually work, perhaps he only makes improbable things likely to happen (think the fullbring dude with the brass knuckles or marvel's scarlet witch) or, as his dialogue with yachiru seems to imply, he plants a suggestion in his foe's mind and they are destroyed by their own thoughts. this would make a case for rose and kensei surviving as their death would have been a mere suggestion planted in isane's head.
kenpachi will probably just muscle past whatever is thrown at him.
that said, i could care less for rose and kensei though i wish kensei's relationship with that one vice-captain whose name i can't rememeber was developed properly.