Marin Lightbringer is a Prince. A half angel, actually, his father being the king of the largest kingdom of Celestia.
He's also a bastard and the youngest son. There was never a chance he would come close to the throne... that is, until his older brothers died suddenly, leaving him as his father's only heir.
Nineteen years old, and having scarcely left the material plane to visit his father's home in Celestia, Marin finds himself dragged there as the new Heir Apparent, and an insistence that he produce heirs of his own. He has his pick of all the noble girls of the kingdom, but there's one problem with that.
Marin is gay and thoroughly unwilling to cooperate with anything that would require him to marry a woman, let alone fuck one.
That's no issue to his father. He'll find a workaround. The royal line must be secured.
Marin's father, King Anthol Lightbringer, is a powerful man. As an angel king, he has the ear of the gods. While any wizard could probably spin up a transmutation for what he needs, Anthol wants a more permanent solution.
Which brought him to the feet of Allimae, the goddess of Fertility. She didn't even want anything from him with his Kingdom; all she wants is the right to use Marin's new womb how she wants, which Anthol will gladly give to ensure his line doesn't die here.
He doubts Marin will mind so long as he is able to continue his studies. He's a scholar above all else. Arcane and religious research was what he was planning to dedicate his life to before this new... issue. Nothing much else has seem to matter to the boy, so Anthol doesn't feel bad for bargaining with his body.
Finding him a man to be his husband of noble enough blood is... more difficult.
But manageable. Floren Heartflyer is nearly a decade older than the King's youngest, and now only, son, at twenty eight, but he's known to have an much interest in men as women, and is of a very well regarded family; a youngest son himself.
So it proves an easy marriage to arrange.
And Allimae's blessing shows itself nearly immediately. Scarcely a month into their union, Marin's petite body shows a small swell of child. At the time only Marin seemed concerned at the apparent speed of the growth- is the baby developing more quickly than normal... or is there multiple there?
He only grew more as time passed, as it clearly is multiple. A blessing from the Goddess of Fertility indeed. Marin won't know how many until it is time for the birth, but he's looking full term with a singleton only a few months in...