Hinagiku is sometimes referred to as being rather masculine for a girl by other characters in the series. Miki suggests this is because Hinagiku is seen as being "cooler" than the boys, and the fact that she was rather domineering at a younger age. Her athleticism, competitiveness, and leadership position all also probably contribute to this view. Despite having such strong traits, Hinagiku is actually terrified of heights.
It is later revealed that Hinagiku suffers from a past nearly identical to that of Hayate. She, along with her sister, had also been abandoned by their biological parents who left them with a debt of 80 million yen (approximately $660,000 US) shortly before Hinagiku's sixth birthday. Following this, her sister, Yukiji, managed to pay off the debt, and the two of them went to live with the Katsura family, as Mr. Katsura had been Yukiji's elementary school teacher.
In episode 13 of Hayate no Gotoku Season 2, the final episode of 'Hinagiku Arc', Hinagiku finally realizes that she is deeply in love with Hayate. This is parallel to the manga at chapter 98.