From ShoujoMagic:
There is a legend in the kingdom of Paros -- a legend of the Sword. It is said that if one who is unfit to rule should wield it, it will mean the ruin of the kingdom. As sole heir to the throne of Paros, Princess Erminia must accept the Sword and a husband when she comes of age on her next birthday. But the princess refuses to wed any man who is less of a man than she -- which excludes every man in the kingdom! Just when Erminia is ordered by her father the king to wed her foster brother Yurias, she has a fateful encounter with the unfortunate, beautiful maiden Fiona..!? "The Sword of Paros" is a miraculous romantic fantasy about defying convention, transcending gender and status, and knowing oneself.

In ancient times, the King of Paroh is savagely murdered with his wife and servants in his castle by mercenaries from the Gohra army. Only his children, Prince Remus and his twin sister Princess Linda, managed to escape during the massacre in the surrounding forest. Quickly caught up by bloodthirsty murderers, they are saved by a strange-warrior with the face of a leopard. Suffering from amnesia, the mysterious savior only remembers his name: Guin. Twins explain him their situation and decide to help Guin hoping to learn more about its origins. On their way, they meet some allies including a young girl from an ape-people, a mage and a mercenary by the name of Isht Van. The small group will rally the tribes Sem and legendary giants, the Lagons, to expel the invaders and to avenge the massacre committed by Gohra.

From ShoujoMagic:
There is a legend in the kingdom of Paros -- a legend of the Sword. It is said that if one who is unfit to rule should wield it, it will mean the ruin of the kingdom. As sole heir to the throne of Paros, Princess Erminia must accept the Sword and a husband when she comes of age on her next birthday. But the princess refuses to wed any man who is less of a man than she -- which excludes every man in the kingdom! Just when Erminia is ordered by her father the king to wed her foster brother Yurias, she has a fateful encounter with the unfortunate, beautiful maiden Fiona..!? "The Sword of Paros" is a miraculous romantic fantasy about defying convention, transcending gender and status, and knowing oneself.