Granny Weatherwax has broken up with her husband, who she discovered had been cheating on her with various women all through their 40 years of marriage. After killing him, she drowns her sorrows in the bottle. In her drunken stupor, she decides to place a curse on all wizards, in a foolish and misguided attempt to punish them for her agony and teach all cheating husbands a lesson to stay faithful to their wives.
Witches and wizards are commonplace in society, and use their mana to perform magical spells. Anyone can use magic, and most people recieve some form of training in school. Unfortunately, there are no spells for birth control. Conceiving a child comes with consequences for both parties. The female suffers the usual physical affects of pregnancy, but her magic remains unaffected. For the male, however, it is the opposite. Although he suffers no physical effects, his mana supply is drained depending on where the fetus is in development.
At first, the drain is miniscule and barely noticeable. Over the nine month period, his mana supply continues to decrease. This leads to a significant drop in magical ability. Naturally, the more babies in the oven out there attributed to him, the more his mana decreases. After a child is born, his supply slowly increases over the next few months to where it was.
1000 years later, the curse is still in effect. Would putting a consequence on men during pregnancy force them to remain monogamous and prevent infidelity among them?