Chizuko's aunt is actually the wife of Shoji Mikamo, the younger brother of Chiko's father, so she and Chiko are not related by blood. She is responsible for slowly poisoning Chiko with food containing lead in order to take control of Chiko's fortune. While her husband initially supported her plan, she poisons him while Chiko is with Nijū Mensō's group and he dies of lead poisoning. When Chiko returns, she continues to try to eliminate her niece in various ways, though Chiko always manages to elude her. When Tome learns the truth behind her actions, Tome successfully blackmails her into giving Tome full guardianship of Chiko and a mansion for them to live in. Chiko's aunt gives up trying to kill her niece after Akine threatens to reveal the truth to the media following a failed assassination attempt on Chiko; when she asks if Chiko still hates her, Akine replies only that Chiko likely pities her aunt. Yoshie is aided by a lawyer named Kurosaki in her attempt to take Chiko's fortune.

(Source: Wikipedia)