Izumi is a shinigami who appears later in the story. In the anime, Izumi's background story is not mentioned and he is portrayed throughout as a cold-hearted character, sometimes almost as an antagonist.
In contrast, he is a tragic figure and has an understanding personality in the manga. He was a 6-year-old boy whose mother hated him. When his father died, his mother lost her mind and beat Izumi for growing up to be like his father. When she beat him, she thought that she was scolding his father for leaving her. In an effort to make his mother happy for once, he ran off while they were out shopping and stood in front of an oncoming train. He saw his mother smile as he was hit, but somehow it didn't satisfy him even though he believed that it was what he wanted to see. Later on, his mother died and Izumi went to take her soul, telling his mother that he had became a shinigami. Eventually, Mitsuki's gentleness makes Izumi realize that he had wanted his mother to call his name while he stood on the railway tracks.
He was once Meroko's partner in the Pediatric Death Ward. Meroko loved him, but he did not return the feelings. Tired of her frequent declarations of love, he tricks her into accepting a new partnership by sending her to train newcomer Takuto in his place. When Meroko falls in love with Takuto, Izumi realizes that he loved her and spends much of both the anime and the manga trying to get her back.
He is, at one point, captured by Sheldon and is tortured with memories he forgot as a human. He tricks Mitsuki, assisting Sheldon. Sheldon tells Mitsuki, "Everytime he touches your pure heart, he realizes how stained he is, and it hurts him." He has only one memory left, but is afraid to see it, because if it will not offer him salvation, nothing will.
In the end, he recalls the memory, and sees that his mother is smiling through tears of guilt and relief, watching him die and thinking he must escape from her. She also reveals that she had to tell herself not to call out, and that she was sorry for not being able to love him. In the end, Izumi resolves to protect Mitsuki. At the end of the manga, he and Meroko team up again as angels.
He likes to call other characters by nicknames (Mitsuki is "Miki/Micky"; Takuto is "Tak-kun"; Meroko is "Me-chan"). In the English manga, however, Mitsuki is the only one he addresses with a nickname.
