Question: In the anime *Hunter x Hunter*, Alluka Zoldyck is considered as a girl by Killua, shown when they leave their estate and were accompanied by four butlers. Killua shouted to Gotoh and said that he needs a female butler to join them because Alluka is a girl.

However, I am confused because Milluki address Alluka as a brother, in the episode when he wished to Nanika to kill the tourist photographer. He clearly told the the tourist that he was just taking his brothers for a walk. In addition, the [Hunter Wiki](http://hunterxhunter.wikia.com/wiki/Alluka_Zoldyck) acknowledged Alluka as a male.

What is Alluka's actual gender?

Answer: 
Alluka is male. He just dresses like a girl.

From [Alluka](http://hunterxhunter.wikia.com/wiki/Alluka_Zoldyck#Gender_Ambiguity) article on Hunter x Hunter Wiki (emphasis mine):

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> There is conflicting information regarding Alluka's gender.
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> **The official data book lists Alluka's gender as male**, and two of Alluka's brothers, Illumi and Milluki, refer to Alluka as their brother.
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> However, Killua, the person closest to Alluka, specifically states that Alluka is a girl and refers to Alluka as his sister multiple times. While Alluka may have been designated male at birth, Killua's interactions show that Alluka may identify as female.
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> This inconsistency may be due to Killua's intimate and understanding bond with Alluka, hence he would know and care that Alluka identifies as female, versus Illumi and Milluki's cold and dehumanizing attitude toward Alluka.
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> 
> 

In the episode showing Alluka in his childhood, we can see that he used to dress like a boy. He ended up looking like a girl, because he played with doll too much that his parent decided to dress him up like a girl.
He is physically a male, and mentally female. It is the reason why Killua referred to him as "she". This is stated in the databooks and also by the canon writers. So in other words, Alluka is transgendered. Though, I believe people have the right to think of him as whatever they like, male or female.