User blog comment:Lex wa Kaiho/What is Lumen Histoire?/@comment-36.74.22.61-20140208032339/@comment-77.242.116.97-20140429125229

could it be that Lumen Histoire is the light part of Zeref? Zeref and Mavis were on good terms with each other.... were. maybe they are hiding his light part, to protect it from the darker half of zeref, until the right moment to awaken it. this also could explain the 2 different explanations: Ivan saying it is the darkest secret of Fairy tail, and Mavis telling it is fairy tail's light.

Maybe Zeref helped Mavis making the guild of fairy tail before turning dark. his light side is then the light of fairy tail, but it is still zeref, and that would be a pretty dark secret if zeref made fairy tail.

also i dont't think it has something to do with 'the one magic', as Hades was searching for the one magic. he knew what lumen histoire was. if it was the one magic, then why would he travel all over the world to search for clue's about it.