User blog comment:IamJakuhoRaikoben/Chapter 418: Challenger, Review./@comment-67.211.8.17-20150202171909/@comment-76.161.172.226-20150202193203

I've always counted the "X791 arc" as part of the Tenrou Island arc. It's essentially the epilogue of the Tenrou Island arc. All it does is wrap up the fall out of the final events of Tenrou Island, it isn't really it's own thing.