User blog comment:Omega natsu2/Tartarus Arc: Part 3 - King of Hades/@comment-18108945-20140330005914/@comment-24066070-20140331201239

Hahaha

Imagine Faust coming over to Earthland and becoming a demon. Faust was already old so the additional 7 years were too much and he ended up as a skeleton, there we have the explanation of Keith's origin.