There's a fair amount of Elsie fanservice going on.
For her demon / spirit hunter uniform (pictures available elsewhere), there are a lot of moe points:
Thigh-high stocking + skirt combo
Detached sleeves
Moe points for her character:
Eye blush
Dojikko
Deredere
Fanservice (maid and student uniforms for her)
Imouto (sort of)
She doesn't seem like a demon at all; she is more angelic - just look at any of her pics!