Everyone expected Harry Potter to be kind and soft spoken like his mother, with just a dash of his father's mischief and bravery. They forgot his grandmother was a Black.

Throughout history the Black Madness had been well documented, even in recent years there had been two notable cases. Bellatrix Lestrange and Sirius Black. Both recklessly devoted to those they loved, both with hot tempers and a violent steak, and both known for causing unbelievable chaos and carnage. Throughout history there were countless other cases, whether the victim in question fell to the Dark Arts or not was really just a toss up, what wasn't, was that they were all brilliant, powerful, and completely lacking in normal human boundaries.

One and all, the victims of the Black Madness were harbingers of destruction, no matter if they were Dark Lords, the followers of a Dark Lord, or even fighting on the so-called “right side” of history. Those that suffered from the malady would eventually reach a breaking point, and when they did, it was a terrifying sight to behold. In hindsight, we can see that Bellatrix Lestrange broke the day she was forced to marry the much older Rudophous Lestrange against her will. Sirius Black broke the night he found the Potter’s dead in their home. Even Walburga Black didn't break until she caught her husband Orion Black with another woman. Without fail, when a victim of the Black Madness breaks, only violence will follow.

Looking further into the history of those who fell victim to the Black Madness we can see a pattern in the history of childhood abuse and neglect they suffered. In previous cases, that was at the hands of their magical relatives that went too far disciplining the victim or were themselves a victim of the Black Madness. Is it any wonder that Harry Potter, a boy raised without love by abusive muggles would also fall victim to the Black Madness when he carried their blood in his veins?

(This was inspired by wondering what a different kind of Dark!Harry would look like, one where he wasn't an unfeeling clone of Tom Riddle, but was hot-headed, passionate, and a lot closer to canon Harry, just a bit more unhinged... and of course with Charlus and Dorea as his grandparents instead of Fleamont and Euphemia)