<Li> Kal So - won as child Se - hwa </Li> <Li> Shin Eun - soo as teenage Se - hwa </Li> <Li> Lee Min - ho as Kim Dam - ryung / Heo Joon - jae <Ul> <Li> Jeon Jin - seo as child Kim Dam - ryung / Heo Joon - jae </Li> <Li> Park Jin - young as teenage Kim Dam - ryung / Heo Joon - jae </Li> </Ul> The town head and son of a magistrate in the Joseon era who fell in love with a mermaid / A modern - day con - man who uses his looks and wit to transform into different people and conduct scams . He eventually met a mermaid whom he fell in love with again in his present life . </Li> <Ul> <Li> Jeon Jin - seo as child Kim Dam - ryung / Heo Joon - jae </Li> <Li> Park Jin - young as teenage Kim Dam - ryung / Heo Joon - jae </Li> </Ul>

The legend of the blue sea actor name