Hazuki is the mother of Mitsuki Koyama and the daughter of Fuzuki Koyama. In the anime, she was portrayed as a caring and confident girl who wished for her and Aoi's child to be a girl. She wanted to name her Mitsuki, hoping that the child would shine forever like the moon. She felt it was a waste not to use the song from the music box and decided to name it "Eternal Snow," which became Route:L's signature song. Hazuki and Aoi's love story touched everyone's hearts.
In one episode, Mitsuki asked Wakaoji-sensei about her parents. He mentioned that Mitsuki resembled her mother in many ways. Hazuki was known for her kindness and willingness to help others whenever possible. Like her daughter, Hazuki was physically weak and often fell ill. She bore a striking resemblance to Mitsuki. Hazuki passed away when Mitsuki was still an infant.
Despite her mother Fuzuki Koyama's objections, Hazuki married the musician Aoi Koga. When she became pregnant with Mitsuki, Hazuki ran away from home because her mother feared that Hazuki’s frail body wouldn't survive childbirth. In the anime, Hazuki made only a few appearances, mostly in flashbacks where she attended Aoi's concert and received the music box now owned by Mitsuki. She agreed with Takuto that Mitsuki was a perfect name for their child.
In the manga, Hazuki died in a car accident shortly after Mitsuki's birth. However, in the anime, Hazuki died during childbirth due to her weak physical condition. (Source: Full Moon Wiki)
