Redo: Mikan, the Princess of the Sea

A 5 year old mermaid namely Yukihira Mikan lives in a kingdom. In their kingdom, they have 2 rules. (One) when a Mermaid or Merman turns 16, they are given the chance to explore the Human world and (two) they are not allowed to visit the Human world until 16. But an unexpected encounter happened that lead them to like each other. Unfortunately, the king found it out.