Kyoko Shirai (白井杏子 Shirai Kyōko) is the principal of Furoboshi Private Elementary School. She unwittingly became the host of Dark Lugiel prior to the start of the series.
Prior to the beginning of the series, when the Ginga Shrine burnt down, Kyoko stumbled upon the Dark Spark in the rubble. Not knowing what it is, she picked it up and was immediately possessed by its dark powers. From time to time, when Kyoko was unconscious, Dark Lugiel would seize control of her body for his own purposes, as he was weakened after his confrontation with Ginga during the closing stages of the Dark Spark War.
Hotsuma Raido eventually confronted her about this fact, while she initially denied it, Hotsuma showed her the decisive evidence - the mountain of Spark Dolls being kept in her room behind curtains. She finally remembered what she did and went into shock. Hotsuma proceeded to purge Dark Lugiel's influence out of her body, and there was an intense struggle. Finally, the Dark Spark came out of her body and apparently disappeared, leaving Hotsuma and Kyoko exhausted.
Unfortunately, in the final episode, it was revealed that Lugiel still had control over Kyoko herself, forcing her to summon him after knocking everyone unconscious with the Dark Spark's powers. However, Kyoko managed to fight its possession and bring out the inner light from within her, and assisted everyone with the revival of Ultraman Taro. As a result, the Dark Spark vanished from her hands, and a Ginga Light Spark took its place.
After the final battle, Kyoko is seen looking on at Ginga's departure.