Board Thread:Questions and Answers/@comment-25951143-20150101110046/@comment-4896558-20161019143728

Olivemeister wrote: So, since Viz is apparently relevant and is information that is considered canonical to the wiki, here's this.

I guess we can concede to the fact that Alluka is a sister to Killua and the Zoldyck family, because Viz confirmed it on their official website.