From MangaHelpers:
Superpowers are now common among the world's population. The manifestation of powers is known as Girls' Witch Syndrome, and the origin of the sudden large scale bestowal of extraordinary abilities to children is an entity named the Mother Witch. Ayumu Takenami carries the title of Brave Star as the top ranking CARD member.
CARD is an organisation formed from the children and girls that have superpowers. After he dispatches armed kidnappers with his bare fists somewhere in the Middle East, Ayumu drops everything to go see his crush in Japan. Yuki Saimiya is an average 17 year-old high school girl with insignificant powers but wishes she could be more like the rumoured Brave Star.