A Euphoric with the ability to turn herself into a living diamond.
Koganei was the wife of a talented artist who gave her diamonds to make her happy, but he hung himself after taking out an insurance policy to give to his wife. Since then she has become obsessed with making her body into a shining monument of his love for her. Eventually she joined the Roppongi Club and was kissed by Kagura. The Euphoria virus made her fetish come to be by giving her the ability to become a living diamond. Now a creature of lustrous beauty, she proudly flaunts her transparent and shallow nature. Due to her powers she constantly craves diamonds to satisfy her hunger. She mostly used all her husbands money to purchase diamonds and eat them. Her hunger for diamonds eventually caused the bank to reposes her house.
Suitengu decided to use her to retrieve Kagura and kill Saiga. Tsujido, Niihari, and Makabe picked her up and drove her to the red light district of Tokyo where Kagura and Saiga were hiding in a night club. After Kagura was finished singing Koganei revealed herself to them and removed her clothes to use her Euphoirc ability. Saiga tried to use his ability on her but was unsuccessful due to her body being transparent. Saiga's friends distracted her while he and Kagura escaped. She and Tsujido followed after them through the various nightclubs. As they were escaping by motorcycle, Madame Koganei got a ride from one of the SUV's she rode in with Suitengu's men and chased after them. She then used a Submachine gun to destroy their bike. Saiga was able to destroy the SUV she was riding but discovered she was unharmed and was rolling towards him. She then used her claws to pierce through the motorcycle and into Saigas chest. After crashing she was going to finish Saiga off but Kagura told her she would go with her only if she spared Saiga. Madame Koganei took Kagura and hitched a ride back to her house. Later Tsujido and his men arrived to look for Koganei but only found the injured Saiga. Saiga was able to get up and threatened to kill them if they didn't return Kagura. Tsujido then received a phone call from Koganei who demanded money in exchange for Kagura. Hearing this Saiga left to go and save Kagura from her. Tsujido decided to not interfere and let the Euphoric kill each other.
At the mansion Koganei and Kagura waited for the money to be delivered. Koganei tells Kagura about her husband trying to break her in to believing Saiga will not come for her. Kagura tells her she fells awful about what happened to her husband and that it was her greed that caused him to die and that there is more to life than things. Koganei tells here there isn't and reminds her of what she did at the club causing her to cry. Soon the lights go out and Koganei grabs Kagura and holds her elongated nails to her throat as Saiga walks in. Saiga tries to convince Koganei to use him to receive more money but she refused. Koganei then tells Saiga to put his camera on the floor and to move forward. As he walked closer he opened his coat to use the high flash of a camera to blind her. As Kagura escapes Koganei goes after, but Saiga sprays red paint on her so that he can use his flash on her. Saiga then use his camera and is able to shoot her right arm off and crack parts of her body as she falls in pain Saiga and Kagura leave.
She then walks outside her house only to find Tsujido, Makabe, Niihari, and Suitengu arriving at her home. She begins to apologies from what happened earlier. But Suitengu says her warranty has expired. Hearing this she hurries back in to her house to escape Suitengu as he follows after her. She then asks him to help her but he only says "dull diamonds have no value", as he pulls his gloves off. She begins to escape but is too late as Suitengu shatters her to pieces. With one last scream she falls to the ground. Her last remaining scene shows her eye as it sheds a tear. Suitengu then ordered Tsujido and the others to collect her broken body and convert it to cash.
Due to the Euphoria Virus Koganei can turn into a living diamond. In her diamond form Koganei is indestructible and is resistant to anything. She also can extend her fingers into sharp claws.