Mulgeopume Ppajin Goemul

The third prince, Rainier, whom the Mermaid King loves the most. Obsessed with the desire to become human and see beautiful flower fields, he goes to the deep sea magician Baller, and the magician offers to use his energy to turn him into a human... But the tummy is full of turmoil. This is the human body the prince wanted. Can he trust him, who somehow gives off an ominous aura?

(Source: Mr.Blue, translated)