This isn’t so much a full system as an interesting bit of math that popped into my head on reading Harbinger’s post about Birthright. It’s essentially an averaging function for settings like Birthright where certain characters (hopefully PCs) have some potency of blood that sets them above others. Maybe the high fantasy world’s rulers really do have a divine inheritance. Maybe the modern occult world’s sorcerers are carefully protecting a flickering fire in the blood from ancient Atlantis. Maybe the supers world’s mutants breed true, and everyone wants to be descended from the really potent heroes.

It’s an exercise for the GM to make sure to avoid the obvious pitfalls in this kind of idea that would make it come off as really racist 🙂 .

## The Math

The math is very simple: when two individuals have a child, average the magical power stat appropriate to your setting.

• If your setting expects power to be something that can be maintained for generation after generation (at the cost of a little inbreeding), round fractions up. That is, in slightly uneven pairings, the kid will tend to maintain the stronger parent’s power.
• If your setting wants a really, really inbred nobility and power that fades as soon as a dynasty is broken, round fractions down. In even slightly uneven pairings, this will mean a permanent decrease in the power of the next generation that can never be repaired.

The bigger your power stat gets, the more generations you can have before simple rounding math tends to cause dalliances to weaken the line down to nothing. That is, if your power stat only goes up to 10, rounding down is often much more detrimental than if it goes up to 1000.

But, honestly, the math is probably something that happens in the background when you’re setting up NPC family lines, and maybe a roleplaying pressure on powered PCs to choose between their One True Peasant Loves and those unlikeable but well-bred marriages their parents arranged for them. The idea is to mathematically back up a culture of inbreeding and insular nobility. It’s not just superstition: that family that can’t clot can move mountains with its powers.

## Revitalizing the Line

Even in an averaging up system, unless the setting is about how far the mighty have fallen since the golden age when the blood was still strong and men had not faded, you’ll need a way to put high numbers back into the system. Possibilities include:

• Boink with Greatness: Sometimes the gods (or inexplicable beings of similar import) walk the world, and they have the highest possible power stat. The kids they leave behind would average out half the highest possible stat even if they’re from some powerless peasant, and they’re even more powerful if someone from the nobility can arrange a liaison.
• Throwbacks and Wellsprings: Sometimes, inexplicably, a normal person is born with an abnormally high power stat, or gains one from an event that can’t be reproduced. Maybe it’s because the magic genetics aren’t fully understood, and a high power can become dormant only to rise up, or maybe it’s just that magic is weird and can sometimes supercharge someone with no particular lineage. Suddenly, a seeming nobody is likely to be elevated to prominence, and may drag friends and family along.
• New King, New Mandate: Sometimes, power is not something that is husbanded, but claimed by conquest. The royalty of the world doesn’t really like to make it obvious that inheriting rulership allows the blood to thin, but taking it by force inevitably results in a new surge of power for the conqueror. History is full of lines that bred their power for as long as they could but inevitably waned until a distant cousin or total nobody raised an army, sat the throne, and started a new dynasty to start the cycle all over.

## Blood Magic Weirdness

• The story of the Countess of Blood is an oddity for most, but a cautionary tale for the nobility. Of course you can maintain your youth and beauty by bathing in the blood of the young and beautiful. You can take all kinds of useful traits in a similar fashion, if it strikes your fancy. But each time you do, it’s like you’re born again as child of your former power and the power of your victim; if you bathe in the blood of peasants, each bath halves your power. The only way to perform the ritual without loss of power would be to murder someone of equal or greater station, and anything you could get from a peasant isn’t worth the permanent cost in power.
• They say that in the early days, potent blood led to a form of immortality. The first kings never truly died, they simply slept in their tombs and mystic isles. If those stories are true, in these days of weakening blood, we must fear that someday the ancient royalty will wake, find us wanting, and reclaim their birthrights. The early days were not nearly so enlightened as our current age, so pray that these ancient warlords do not rise up.
• You think I don’t want you to be happy. That I’m just trying to protect our family’s power, and that’s why I don’t want you to marry your peasant love. It’s true, your child would be half as powerful as you are. But it’s worse. That level of drop in power is much harder on the parent that doesn’t have power to bring to the tryst. I’ve heard stories of noblewomen that sucked the life out of their strapping peasant lads to conceive, and noblemen whose peasant brides couldn’t survive the birth of a powered child. It doesn’t happen every time, mind you, but it happens much more than you’d think, and much more than normal breeding. Do you want to risk that your lover will be lucky? Or do you want to do the right thing, breed within your station, and allow your low-born love a long life with a spouse that’s equally bereft of power?