Hearing Sarina's question, the three girls were wondering whether or not to answer that question. After a brief thought, Xie Xinyue decided to answer, as Sarina and Mia were already friends with a member of the blood race. They had a right to know about Ivy.
"The blood race is a race of nocturnal beings that drink blood from humans. But each of them has a kind of criteria to do that, they don't choose anyone. Men of the blood race choose virgin women for this, normally, these women end up becoming partners of these men. While women of the blood race choose men and women, when they choose men, they will only choose one man for their life.
As this girl named Ivy always drank Liu Yang's blood, she chose him as her blood partner for her life. This is no different than marriage and a promise between the two. But she still agreed to share Liu Yang with you two, for a noble of the blood race, she is more flexible than I thought.