Vander Decken IX is the descendent of Vander Decken the first, an insane pirate who crashed on Fishman Island hundreds of years ago. He is a Fishman but seems to have no I'll will to humans. He will harm them if it pleases his business partner though. He is a clingy obsessive man who becomes easily attached to a love interest. He will stalk them for years if needed and would try to kill them if rejected. He'd rather they be dead than love someone else.