She's cute and I love her design. Small frame but not flat, long purple hair, the cowlick. The ninja clothes are great, too.
I like how she sometimes plays the straight man to Rance's antics.
She's feminine and is not a shameless seductress like other girls. I love how she does many things while being absolutely embarrassed; her vow of loyalty to Lia and her clumsiness throw her into interesting situations.
When her usually stoic self breaks down and her true feelings come out it makes me want to protect her. Getting to that point requires some bullying though, which is nice in moderate quantities.
So... Because she's a tsundere in a world of derederes?
Reasonable. Variety and differences is key in character design.