Changing yourself is not an easy task. It requires weeks, months, years of dedication to becoming a different person. Or, Percy Weasley thinks, I can just make a potion... Rated M for murder of an unknown person committed by the main character.
What was Percy Weasley thinking and doing through the end of the First Wizarding War to the end of the Second Wizarding War? Canon up until the seventh book. No romance.
Harry noticed it in his first year, then in his second, and figured it out in his third. There's something about the Weasley twins...something not quite right...something beyond their brotherly bond. Harry's nose won't let him forget about it.