Hiou, Shizuka

Shizuka is a pureblood vampire from the Hio family. Shizuka usually appeared as a calm and composed woman but is always smiling as if amused when taunting people. Even for a pureblood, her fellow vampires felt uneasy around her and referred to her as the "Mad Blooming Princess" by her fellow vampires. She was locked in a cage and kept in isolation the moment after she was born. Everyone claimed it was to protect a rare and beautiful creature such as herself, due to the Hio family members having a sad history of going berserk. However, when decided to escape with her ex-human lover, his name was put on the hunter's execution list and was killed as a result (even though he hadn't fallen to a level e). She is currently in hiding and is wanted by the Hunter's Association.

Shizuka was the pureblood vampire responsible for Zero turning into a vampire. The people who killed Shizuka's ex-human lover were Zero and Ichiru's parents. Enraged and vengeful, she attacked the Kiryu family, killing both parents, biting Zero to curse him, and taking Ichiru with her. After Shizuka regained her senses, she realised that the mastermind behind this scheme was her fiancé, Rido Kuran.

In order to obtain more power for her revenge against Rido, she planned to enrol at Cross Academy and kill Kaname. Shizuka chooses Maria Kurenai to be her vessel in order to hide her identity when she enters Cross Academy. Maria agrees to loan Shizuka her body both because she admires her, and also in exchange for some of Shizuka's blood, which helps heal Maria's sickly constitution.

Shizuka's blood can prevent Zero from falling to Level E, and thus Yuuki risked her life for Zero to be able to drink Shizuka's blood. However, In order to protect Yuuki, Kaname kills Shizuka. Before dying, Shizuka warns Kaname that he will live in darkness and has summoned a sinister future for himself. Kaname drank her blood and leaves some for Zero to drink as well. Unfortunately, the blood was drunk by Ichiru who arrived at the scene first.

(Source: Vampire Knight Wiki)