Light Yagami/Harry Potter
Light knew what he did had screwed up very badly with Dudley's head. He still holds that he had no choice. If one wanted to survive in the Dursley household as a child, one needed one of two things: Vernon and Petunia's approval, or Dudleys protection. Light knew the first was unlikely to happen. He also did not like the idea of making peace with his abusers. So, second option it was.
And if he was going to do things, he would do it right.
Light couldn't kill Vernon and Petunia Dursley. But he could get Dudley.
That made Dudley very, very vulnerable. Light knew how to fix it too. It would take some time, teaching Dudley to think outside Light's approval. Dudley was now 'family', had been since that day two years ago when he had taken his hand. 'Family' had to be planned around, not over. But Light's life depended on Dudley's goodwill. So it made sense to tie Dudley's goodwill to Light's approval. Sometime down the line, when they were twelve and Light had more maneuverability to get out from under the Durlsey's, Light would fix it.
But it wouldn't be now. Not anytime soon. Dudley was Light's till that time.