Lleviathan is a marine deity in Porth Llaffan in Dragon Quest IX. He resembles a blue whale with a red belly who can understand and speak human dialect and brings fish to the village. As of lately, he has been appearing a lot, bringing fish to the village. Since Dylan disappeared in a storm, his daughter Joan, being a descendant of the summoners of this beast, is asked to calm him down. So the hero follows and sees that the girl, mayor Bryce, and their guardian reach the cliff where the beasts appears.
The first time the hero/heroine and his/her team encounter the cetacean is when they arrive at Porth Llaffan to bring them fish at Jona's petition. When they meet at the cliff, he immediately eats Jona up so they have to fight this monster deity to save her. They defeat it and it spits her out, only to come back at them again but Jona gets in its way and the beast stops. Then it speaks, asking her if they are not with the argumentative and abusive mayor. It is then that Jona recognizes its voice as her dad's, Dylan. He then explains that he looked like Lleviathan because of a golden fruit he took moments before dying, he wished to protect her daughter, so he became Lleviathan and brought fish to the village to keep her well. Jona thanks him but decides to remain at the village, despite his invitation to accompany him.