Everyone who's met Hisoka says, "How can a woman be this much of a pervert?" Hisoka is simply true to her desires. Ever since she was little, she knew that in this world, if you had strength, you had everything. So she kept challenging people and fighting.
When she met the eldest son of the Zoldyck family, who only knew how to complete his assignments, she instinctively started flirting with him. She never expected him to stay instead of getting scared and running away.
"So you're really a pervert. How do you write that symbol you keep using?"
Hisoka pestered him to fight. Illumi merely said, "There's no money in it. Not worth it. I refuse."
So Hisoka handed over her bank card. After getting the fight she wanted, she found that Illumi had put in no effort at all. Frustrated but unable to do anything about it, Hisoka could only keep pestering and harassing him.
Theme: Love is all you need