Kaname & Seiren

Seiren works for Kaname as his unofficial bodyguard. They are also night class students and be often seen together. Seiren is a common vampire, who was once a human. In Memories Chapter 4, It develops into Serien's past and her first encounter with Kaname.

Background
Seiren was originally born as a human girl named Hoshino. She was bought as an infant and raised to become a sacrifice for Kaname Kuran to feed on. When shown to Kaname, she and another sacrifice, Yoruno, gladly offered themselves to him. She believed that by letting Kaname drink her blood, she would be allowed to go to heaven. Instead of drinking their blood though, Kaname rescued both Hoshino and Yoruno by taking them to Cross Academy. However, on their way to Cross Academy, Yoruno ran back, fearing that if she didn’t offer herself, she would go to hell.

Hoshino ran after her in order to stop her, only for the both of them to be caught by aristocrat vampires. While Yoruno died from the loss blood, Hoshino was on the verge of death when found by Kaname. He gave her the option to die or to live the life of a vampire. She chose to live, and Kaname turned her into a full-fledged vampire, while giving her a new name, Seiren. To show her gratitude, she trained in martial arts in order to stay by Kaname's side.

Seiren is often seen with Kaname, thus suggesting that the two do indeed have a close bond. As Kaname doesn't bond easily with others, it is quoted that Seiren is known to be one of the only people (apart from Yuki Kuran) to be aware of Kaname's true nature. It is apparent that Kaname trusts her deeply. Seiren has proved her loyalty to Kaname many times, risking her life to spy for him and protecting the Day Class students alongside Akatsuki Kain and Ruka Souen. In the 72nd Night, Kaname has been seen with Seiren even after his murder of another pureblood vampire.