Asuha is 10 years old, like Lotte. She became Lotte's best friend.

Spoiler

In reality she is the daughter of Naoya and Queen Mercelída, the "dead princess" Asuhariet, princess Astarotte's older half-sister (because succubus pregnancies are shorter). She doesn't know her mother is the Queen and Lotte her little sister. She has an adversion to underwear (she is half-succubus after all), and would very much rather go commando, much to Naoya's chagrin.