Nagasaki prefecture, in Japan, is a magical kingdom. While the wizards that live there are unable to cross the ocean, and are trapped in Kyuushu, they still pose enough of a threat that Americans dropped the bomb on them during WWII. The residents are worried that this will happen again, especially if the regular humans decide magicians are a threat.
Daughter of the most powerful wizard alive, Mizukura Risuka is ten years old, and living outside Nagasaki, searching for her father and killing evil wizards. Her blood contains spells that control time, and allow her to fast-forward her own life. Her ultimate technique kicks in only when she dies bloodily -- her blood will reform into herself at 27, at the height of her powers, for one minute.
Her guide through the world of normal humans is Kugi Kizutaka, also aged ten. Kizutaka is a genius, and a sociopath. He believes the only way for people to be happy is to be ruled by him and views everyone he meets as a potential pawn, or slave. Including Risuka.