Thread:RuneLai/@comment-30473998-20180614015511/@comment-1327106-20180614063436

Generally speaking you should only use official sources, such as the manga and guidebooks. On occasion we allow other sources for the Trivia section.

For that particular entry, reference 5 is only in regards to the writing, which is also cited in the manga itself. Notice that it's a companion to reference 4 and doesn't appear alone. Reference 5 illustrates how the trivia works (for those unfamiliar with katakana), has its own references for further examination, and provides an in depth explanation that the wiki itself doesn't have room for.

It would be a problem if reference 5 was linked in the article itself, but because it's a "bonus" in the Trivia section it's okay.