I tend to mistake the three sisters so far as i understand it Xue´er was the one of the three who was first in line to inherit the Palace Master position right ? if so then its in the Spoiler Below if not ignore the Spoiler and excuse me for dropping it in Spoiler Point 1, She got intrigued by how her other two sisters got into him Point 2, he fought her later on after he returns with Tianer, and tricked her into a promised Marriage and he "beat" her in the fight and played it like he payed a high price for it as he took an her sword head on. Point 3, as they enter the Dimension with the Dragons she tells him that she lured him there to help and he just says that this is only Natural to share her Burdens and this is the moment where she totally falls for him.