Light Yagami/Harry Potter
Dudley burrowed his head in the carpet spoke something softly unintelligible.
"I don't read minds, Dudley," Light reminded him and Dudley raised his head slowly.
"I said, I can't read," the four year old spoke. "Or write properly. Or count."
Oh. Well. That. Light could do all that and more by three but Dudley wasn't Light. Light felt the need to remind his baby cousin of that fact.
"You're four," Light said gently. Which was as gentle as Light could be without saying that Dudley was a normal human idiot and not a genius. Not that Dudley knew Light was a genius. He was just vaguely aware his cousin was better than him somehow.
"But everyone can do one or the other," Dudley whined. "Then they call me names."
"Your parents call me names," Light countered and Dudley scoffed again.
"You call my parents names too," Dudley replied with childish logic. He wasn't wrong. Light did call Vernon and Petunia names. "And now you're calling me names too," Dudley whispered.
Light blinked because- what? when?
"I don't," Light refuted that accusation. There was no point in calling Dudley names. Light was an adult, Dudley a child and thus, by definition, Dudley shouldn't know better. Light refused to go that low, calling children names. He was a mass murderer, he had standards, thank you very much.
"You called me Dudley just now," Dudley said with all the logic of a sage. "One, four, three times. Not Diddykins."
A warmth settled in Light's stomach, low and burning, same as when Sayu called him 'Onii-chan' that first time.
"Sorry, Diddykins," Light said and let go of his grip on his cousin. "Won't do that again." He offered a hand to the boy on the floor.
"You better," Dudley grumbled and took Light's hand.