Liala

Liala was born the single daughter of a Demon family with the rank of duke who had produced many Demon Lords in the past, although born with the appearance of a normal demon, as she grew her appearance increasingly became more like that of the Gods that the Demons were descended from and who were also their eternal enemies.

Liala is almost always seen smiling and possesses a more playful, gentle, and childish demeanor. Beneath that playful spirit, she has the potential to get a bit violent, and is willing to kill in order to protect the love of her life, Her adoptive brother Leohart. She's also very perceptive and has a strong sense of a woman's intuition.

(Source: Shinmai Maou Wikia)