Quote Originally Posted by shinta|hikari
True. Rather than Isley being weak, it just shows that Helen has gotten much stronger than before. Strong enough in fact, to require Isley to exert some effort to kill her.

Quote Originally Posted by Munsu
I think his facial expressions depict that he's struggling in his current state and also surprised by how well Helen is fighting him.
I think that's it.
For some reason Isley doesn't want to go all out if not necessary, thus tries to adjust to the minimum yoki he needs to get results. But he was tricked by Helen and her yoki hiding and surprised she in fact was a lot stronger than the adjustment he made.

I guess that for some reason, he also wanted to remain invisible, and his enconter with Helen may reveal his position, his plans may go to dump thanks to that.

As for Demons, they really look like failed claymore experiments. I don't know why they needed sewing though.