The core tension often doesn't come from the magic itself. It's about narrative scale. J.K. Rowling's universe operates on a more intimate, personal threat level, while Hellsing's Alucard is a walking apocalypse. When you graft that kind of power onto Harry, the challenge is finding a story that isn't just him effortlessly vaporizing Voldemort by chapter three. The good ones use it as a character study in alienation.
His power isn't just a new spell list; it's a physiological and existential rewrite. He might stop aging, need to drink blood, or have the souls of millions screaming in his head. That creates immediate, horrific conflict with the wizarding world's rigid norms. How does Dumbledore, a symbol of controlled, wise power, react to a child who is fundamentally a monster by their definitions? The conflict becomes philosophical: is Harry still human, and does the wizarding world have the right to judge what it can't possibly understand?
Then there's the internal struggle. Alucard's power in Hellsing is deeply tied to his worship of his master, Integra, and a certain nihilistic joy in carnage. Harry, with his ingrained sense of justice and protection, would likely be repulsed by the predatory instincts and bloodlust. Watching him try to uphold his 'saving people' thing while fighting an urge to see every Death Eater as a satisfying meal is where the real drama lies. It often turns the Horcrux hunt into a dark mirror, with Harry wondering if he's becoming something worse than the thing he's trying to destroy.