From MangaHelpers:

Coming from a family of swordsmen, Kamiku Kyotaro was the next in line to represent the Kamiku style. He is forced to leave all that behind when he is suddenly summoned by five sisters into the kingdom of Trekwars. In this world where magic exists, only females are able to cast spells and the queen of that generation has protected Trekwars using her strong magic. However, the queen has become weak and, with that, the neighboring country, Cardagia, has started its invasion. The country needs a new queen so that the protection spell is strengthened. Kyotaro has been summoned to bear a child with one of the five sisters who are princesses of the royal family so that one of them can rise to the rank of queen and protect the citizens of Trekwars. Although Kyotaro has lots of magical energy that makes him the only available candidate that the princesses have, he himself has personal issues about the situation he is put in. [vyc]