The fight for Lucy Heartfillia

Its a typical day in Magnolia until the guild masters from the other popular guilds challenge Fairy Tail. Who will Fairy Tail send out to fight, and what is this challenged named "Nusumu" all about and what does it have to do with Lucy Heartfillia? Please review and help me out on tips and advice! I dont own Fairy Tail or the Cover Image! Nalu and sorry for bad summary.