Natsuki was a Lom Gunji vampire and one of the lieutenants of the Lom Gunji known as "Googly". Her 'degeneration' enhancements were mostly along the lines of highly increased strength and dexterity, in keeping with the general tradition of Googly's followers to have easily-concealed modifications.
She was captured by the Vaxian Empire during a raid on the White Rose University and Aureant Malio and Meriadoch tried to interrogate her. It was discovered that there was a powerful block on her mind, put there by Googly's trusted henchman "Vampyroteuthis Infernalis". There was no choice but to cause a backfiring of this block, which destroyed Natsuki's mind and killed her.