This artificial hand in the shape of a hook is the hand of Giler, the pirate captain of the Epsilons.  Once notorious for pillaging small and large out on the open seas, Giler was defeated by Alberto.  With his pride damaged, he pursued Alberto to the end for revenge.  When his pursuit failed, he made the foolish choice of using Sereness to awake Kraken in the abyss.  He was successful in burying Alberto in the abyss - but not before he, too, was buried in the same sea.