Killua Zoldyck is very fond of his younger sibling, Alluka, and is one of the few characters in Hunter x Hunter who is not afraid of Alluka's special power, which her family calls «Nanika.» This special power is an unstoppable force that potentially threatens everyone around Alluka, causing many people to wish harm upon her.
Nanika is the mysterious «alter ego» of Alluka Zoldyck, the second youngest of the Zoldyck family. Nanika's power is terrifying and limitless, but how exactly does it work, and where did this strange power come from?
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Similar to a parasite, Nanika possesed Alluka and is using her body as a host. Because of this, Alluka has to comply with Nanika's powers and help meet the conditions in order for Nanika's powers to be used. Nanika has the power to grant any wish or request made by someone, but only after three of Alluka's requests have been fulfilled. Once three of Alluka's requests are completed, Nanika takes over to grant a wish. Once the wish has been granted, Alluka returns to normal.
There is a small catch, however; the bigger the wish someone makes, the more difficult Alluka's following three requests will be. The requests become increasingly more and more difficult, until eventually they cannot be fulfilled. If a person refuses to fulfill four of Alluka's requests, that person will die, along with at least one other of their loved ones. The bigger the prior wish was, the more people will die if the next round of requests are not completed.
What makes Nanika such a huge threat to humanity is it's «god-like» abilities. Nanika is infinitely powerful; any wish can be granted, no matter how difficult or impossible the wish seems. If it is wished
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