Board Thread:Questions and Answers/@comment-25951143-20150101110046/@comment-5780397-20150317005904

Yes, but they do not know about Nanika, it is out of disrespect. While Alluka is most likely male (Killua clearly called him his "little brother" at the phone with Morel), Nanika is probably female, that is why he says he needs "her" powers and uses feminine pronouns when talking about them.