Keiko bore similar features to her daughter, Hotaru; She had long, dark hair with a purple sheen and violet eyes.
Manga and Crystal series
Keiko was killed in a fire that broke out when lightning struck her husband's laboratory during his research when Hotaru was six years old. The same fire also gravely injured her daughter. During her life Keiko possessed the Taioron Crystal, which would later be used by Hotaru to soothe her own pains, and eventually become a power source for the Death Busters. While Keiko herself only ever appeared in flashbacks, Hotaru still seemed to hold her in high regard, and possibly objected to Kaolinite trying to pursue Souichi Tomoe because of this.
First anime series
Keiko's backstory was not elaborated on in the story. However, she was shown with her face covered in shadows in a very brief scene when Hotaru recalled her happy memories.
- It is interesting of note that when Mistress 9 aged Hotaru's body to that of an adult woman after gaining control over her, she bore a striking resemblance to Keiko. As it was Hotaru's actual body and not an assumed Daimon form of Mistress 9, this indicates that Hotaru will grow to strongly resemble her mother when she reaches adulthood.