Kyou wa Arashi

"Please let me stay here." Wakana is confused.Takayashiki Yukarino, her classmate, an heiress of the rich tycoon family, came to her house and begged Wakana to let her stay at Wakana's house.
Why did she run away from her home and why did she choose Wakana's house? They barely talk to each other, let lone know each other.