User blog comment:Omega natsu2/Chapter 362: Natsu vs. Jackal, Predictions./@comment-122.52.143.112-20131130010719

Something looks familiar of Jackal's demon form. He somehow looks like a combination of Aki in his S-Class Monster Soul form and a Soul Eater who is an old enemy of the leader of Black Airs from Hiro Mashima's Monster Soul.

Did anybody saw the similarities?

My theory is that some of the Nine Demon Gates members appear to be recycled versions from Monster Soul.