I also have an ameripan idea!!
This one starts with Japan during his isolation period. In this one Kiku and Alfred are still personifications of countries but in this version Alfred is the personification of an wonderful underwater nation that is a combination of America and Atlantis (think fish burgers and underwater Hollywood). Alfred is also a merman as are a lot of his people (mermen and mermaids). However much like the mermaid in the little mermaid Alfred is terribly curious.
One day Alfred's curiosity gets the better of him and he get's captured by Japanese fishermen and is sold to one of Kiku's advisers who in turn presents the strange creature to him as gift. Kiku's adviser hopes that the strange creature (with scales that shine with the colors of the rainbow) will help Kiku with his depression and loneliness. The adviser is worried however that Kiku will not accept the gift as by the time it (Alfred) arrives he is very unwell. (Alfred had tried to speak to his captors but they didn't seem to understand or listen, so sick from being out of the water so long he had given up.)
To the adviser's surprise Kiku accepts the strange creature and insists on nursing Alfred back to health. Eventually Alfred is living in a pool in Kiku's hidden garden in the middle of his palace. Eventually Kiku and Alfred bond despite the barriers of: culture, custom, language, Alfred's wariness and anger at being held captive the two bond. Alfred and Kiku eventually learns how to communicate. Alfred needs to return home but at this point Kiku can not imagine life without Alfred. ( I can see this as also being done as a version of the Nightengale Story)
Kiku has to also worry about other nations finding out about Alfred for obvious reasons. Eventually Kiku realizes that he has to help Alfred return home to his people and country. Trials and Tribulations ensue, with the end result being a happy ending with them finding a way to see each other regularly. Maybe another future adventure could be them finding away for Kiku to come visit freely Alfred in his kingdom.