The plot unfolds beneath the waves of Mer, where an unexpected war erupts between the peaceful kingdom of Bars and neighboring realms, Moslem and Agadia. The rise of Bars, a once inferior kingdom, leaves many perplexed. In the midst of it all, Jo and Oz, two young spiritual knights, support themselves by defeating sea monsters, but their society views them with suspicion and apprehension. Despite their aversion to conflict, they become embroiled in the battle against Bars' army and the dark forces leading it.