I'm just waiting for the day that Succi-chan brings the Vitality Monster home to the succubi world and he instantly subjugates everyone except for her; because she's the only one capable of withstanding it, even out-classing her mother.
Her grandmother's explanation could be used as justification as to why the other succubi all look like crackwhores, while Succi-chan is thicker than a bowl of oatmeal. Something along the lines of "having multiple victims reduces the quality of the life force energy they receive."