In ancient days a bargain was struck between the fey king Alaconte and the kingdom of Naia: every seven years, seven young women would be given to him in exchange for his protection and blessing. The seven are never seen again; tradition holds that the seven young women are going to be the bride of the fairy king, which helps the more superstitious come to terms with never seeing the young lady again and gives everyone else a party with which to soften the blow. The seven may be chosen by the government, or volunteer, or be spirited away by fey carriages should the promised time come without the promised number agreed on.
The fey deal has never sat well with the mortal families made to give up their daughters, especially as the kingdom has grown into an empire. The time, seven ladies have been chosen in a political move to remind newly empowered nobles, merchants and politicos exactly who the emperor is. Needless to say, the aristocrats are not happy, and unlike the commoners have the ability to do something about it.
End result: seven young women are given the best education in self-defense that money, power and influence can buy, according to their family's social position and powerbase. Military family? Swords and armaments. Diplomatic corps? Social manipulation and politics. Organized crime? Straight up assassination.
Of course, they are being sent to sent magical fairies from another world, so surviving is less about killing them and more about understanding them and using their nature against them.
This story would probably have a strong start and stumble badly in the denoument, since you'd have to come up with a way to make all of the girls' training useful or at least useless in interesting ways against an alien enemy that uses magic. And plus, you'd have to introduce the "enemy" right at the end and make it memorable...
Title: Game, Set, Gunner
