Maximus saw the flute in your cube, and thought it was something special. He told you that Utsida, a Handicrafting Master in Sanctum, might know more. Utsida said he should fix it first to find out what it is. When you got all the necessary materials, he determined the flute might be able to summon an Acheron Drake, and that you should test it. When you went to the Drake Temple Ruins and played it, a Acheron Drake named Akairun of Medeus appeared.