Yuki and Zero met at ages 11 and 12 respectively, when Zero was taken in by Kaien Cross into his home. Yuki immediately took to the young boy and looked after him the night they met, cleaning the emotionally fragile Zero's wounds. She promised to always stay by his side after she discovered him distraught one night, tearing at his neck. Yuki would often stay up at night with Zero, patting his head when he had nightmares, to help him to fall back asleep. Yuki's nature overcame his distance and her presence helped his nightmares to cease. However, Zero began to act aggressively towards Yuki after learning of her love for the Pureblood vampire, Kaname Kuran, possibly in part due to jealousy. When Zero began to panic, fearing his transformation into a vampire, he accidentally lashed out and hurt Yuki. When he found himself attracted to the smell of her blood to his shock, he swore to the Chairman, that he needed to become stronger. Yuki accidentally admitted she was scared of Zero. When Zero tried to tell her his secret, she revealed her fear about being attacked by the vampire in order to empathize with Zero. Instead, Zero became angry at himself, so he tried to push her away, deciding against telling her his secret. This was the beginning of Zero deliberately trying to put distance between Yuki and himself, to the point where he refused to be adopted by Kaien because he did not wish to become a part of Yuki's family. Yet Zero still grew attached to Yuki and his affection for her grew throughout their adolescence. When Yuki went to see Kaname at the school and was disturbed by the encounter, Zero observantly told her if she was not scared, she would not shake. He is very protective of her, which Kaien used to get Zero to attend school, after Zero stayed back a year of high school and continued to refuse to enter because he despised the idea of vampires and humans going to school together. Zero agreed to attend school when Kaien told him that Yuki would have to be the school guardian of Cross Academy all by herself if Zero did not go to school.
