War on Uncharted Waters

Culbert is the strong youngest son of the human chief and lives on an uncharted island secretly guarded by a tribe of mermaids, and he has been tasked with leading a war against an enemy foreigner kingdom who want the mermaids' magic for themselves. But Culbert is unwilling to let this happen, for his closest friend and love interest is the mermaid chief's youngest daughter, Doris.