The Queen's Knight

When Yuna Lee's mother moves to Germany to pursue a music degree, she's left to stay with her father, a university professor, and her three older brothers, who are fiercely overprotective of her.

During her summer vacation, she visits her mother in Germany, where she falls off a cliff and is rescued by Rieno, an 18-year-old knight living in the land of Phantasma. Rieno makes a deal with Yuna that because he has saved her life, she must marry him and become his queen. Indebted to him for saving her life, Yuna is torn between her normal world back home and life as Phantasma's Queen.

(Source: Tokyopop)