That is a very good question. I like to see girls in peril, but not being hurt. I like to see a sense of helplessness without them being in any "real" danger, or where they could be hurt.
I also like things that are weird, anything that isn't the norm, because it can be boring always being the same. I found out about monster girls and was hooked, i love the reaction someone has when they are transformed, it's distress without any "damage" you could say
I hope i'm being clear, it's not something that's necessarily easy to explain
If you want me to answer anything more specific, please don't hesitate