In Japan, criminals are running rampant, and the law enforcement quality is worse than it has ever been. Anyone who has a large amount of money or is even a bit famous is liable to be kidnapped at any time, and it happens constantly. Bodyguards have become a necessity for anyone who doesn't want to be held captive, and special schools have been created for the soul purpose of training body guards and special organizations called vigilante groups that are made up of of highly trained people with advanced combat skills enforce the law since the police do not.
Asahi is part of a vigilante group called Nekomata, which makes its headquarters in a cafe of the same name in downtown Tokyo. Asahi is still young, but she's the best of the best working in the city, and is very passionate about her job. Then she gets called to a security school and offered a contract to be the bodyguard of the incredibly famous Kisaragi Sakuya, the rich heir to the Kisaragi Group and the youngest person ever to win the Nobel Prize with his incredible inventions. However, all of his previous bodyguards quit because of his personality and rather unfortunate hobby of testing his inventions on his bodyguards. Asahi accepts, and is whisked away from her rough-and-tumble home in Tokyo to a totaly different enviroment: the Kisaragi mansion. Eventually, she mangages to befriend Sakuya, and friendship grows into romance. Now, she must work to thwart the various criminals attempting to kidnap Sakuya, 90% of which want his money and 10% his skill, for if Sakuya were to join a criminal society and invent weapons for them, they would become the best in the world.
Note: Originally used in Emura's W-Juliet II, the sequel to W-Juliet. The characters Sakuya and Asahi are played by W-Juliet's main characters, Ito and Makoto.