Board Thread:Questions and Answers/@comment-25951143-20150101110046/@comment-26871067-20160817060410

I can't believe no one has pointed out that the series' narrative has explicitly called Alluka a girl.

I'm referring to chapter 322, titled "Siblings". The standard (i.e. the actual dictionary standard) spelling for the term is 兄弟, using the kanji for "older brother" and "younger brother".

This is not the spelling used for the chapter title. 兄弟 is considered to not be a gendered term and can refer to any group of siblings regardless of their genders, so the fact that the spelling is altered draws the attention and must be intentional.

The chapter title for 322 is  兄妹, which  consists of  the kanji for "older brother," and "younger  sister. " Seems pretty definitive to me - again, this is the chapter title, which is as objective as narration and is not influenced by any characters' beliefs regarding Alluka. This is in the manga itself - that makes it a primary canon source, as opposed to supplementary/external materials like data books, games, trading cards, etc.