Draco Malfoy is a study in contradictions.
There is a part of Harry's mind that cannot separate him from the rude, insulting git he went to Hogwarts with. The greater part of him, however, is fixated on the person Draco has become.
When he was assigned Draco as his Auror partner, he had braced himself for the worst. But, to his surprise, Draco is nothing like the boy he remembers. He has done quite a bit of growing up in the year after the war. He has transformed into a polite, stately young man, who would not look out of place in the highest of the Muggle royal courts, able to charm even those who truly hated him at Hogwarts.
It is at the annual Ministry Ball that Harry truly realises this new personality of Draco's. He walks tall and confident during the Ball, but it is his dancing abilities that enthral Harry. He is graceful and elegant on the dance floor, but somehow manages to retain an air of danger, almost like a tiger stalking its prey.
Harry is pretty sure that he fell in love with Draco at that moment.
For:
Alphabet Soup: Drabble competition - G is for genteel: having an aristocratic quality or flavor
The If You Dare Challenge, Prompt 93. Reconstitute
OTP Bootcamp, Prompt 46. Diligence