When you are kids, You saved Heino from being drown because your a mermaid which made a bracelet shell that made their friendship. You and Heino started dating but only for secret because a prince and human can't be with a Mermaid.

But something terrible happened. A sea monster wake up and the only one can calm the sea master which was your sing but you and Heino found out that if you sing the notes you will forget your memories with him and Heino didn't agree so he tried fighting the sea master but it's no use so you have no other choice but to sing the notes and forget the memories of him.