Kururu Sumeragi is the leader of the current Tool Toul To and Pledge Queen. She has very messy hair, and uses pins in attempt to keep it kempt. She always carries tools around in her clothing. She is Ikki's Tunner and wants to get to know him better personally and in order to tune him better. Although shy around Ikki at first, she becomes devoted to him after witnessing his anger over Simca's attack. She does not wear ATs, but as the leader of Tool Toul To, she is a true genius in repair, construction, and maintenance of ATs. In Ikki's battle with Ringo, Kururu identified the sound of Ikki's ATs, arrived at the battle in time to intercept Ikki as he was falling towards the river, and rebuilt his ruined ATs in midair in less than three seconds. She originally rebuilds the Wind Regalia for him, though it is stolen and given to Sora. During the Fight with White Wolf Clan, Kururu wants to show Ikki her power as a tuner by helping out the other team. Afterwards, Ikki asks her to create the new Storm Regalia for him, a request which she gladly accepts.

It quickly becomes evident that Kururu has feelings for Ikki. During the talk with Kilik and betrayal of Sora, she ran to him and tried to confort him.Later on, she appeared along with Simca and Ringo (under the guise of Croissant Mask) after Kogarasumaru's special training. Agito teases them, saying, "You three came here with intentions of getting a kiss, but you're out of luck, right?" The three deny this accusation, but then reveal they had some similar intentions. During that time, her power struggle with Simca and Ringo over Ikki's affection is seen.