User blog comment:IamJakuhoRaikoben/Chapter 422: Orochi's Fin, Review./@comment-24784846-20150302212044/@comment-7418318-20150302215049

Considering the partially visible tattoo (guild mark?) on his arm and how on MS he's called sensei and not master, he might have tagged along with them for his own reasons.

Maybe he's after some artefact or magic? Or he could be trying to stir up enough trouble to lure someone from the Wizard Saints out so he can get something he want from that person and Orochi Fin are just convenient tools to achive his goal.