Kaoru is a Level 7 Psychokinetic Esper (the maximum esper potency designation) and also the main leader of the group The Children. It is explained at one point that it was Kaoru that approached Shiho and Aoi in friendship when she was given over to B.A.B.E.L. five years ago and has generally established herself as the leader of the group. Under Minamoto's leadership, Kaoru has opened up to demonstrate that she is a dynamic tomboy with perverted oyaji-like tendencies that loves to have fun and keep Minamoto all to herself.

(Source: Wikipedia)