User blog comment:IamJakuhoRaikoben/Chapter 459 & 460: Weakness & The Alighted Pegasus, Review./@comment-4933386-20151102015600/@comment-7418318-20151102074604

The master of Blue Pegasus (maybe even founder?) Bob is a former Fairy Tail member and they worked well together during the Nirvana conflict, so it seems natural for the two guilds to be close.