While journeying through the Johto region, Satoshi and his companions arrive at Altomare, an island city hosting the Pokémon Water Race. Amidst the festivities, Satoshi experiences peculiar events—losing the race, witnessing a troubling Pokémon attack, and encountering a girl who denies their previous meeting. Unraveling the mystery, Satoshi discovers the girl is actually the Pokémon Latias in human form, alongside Latios, the Eon Pokémon, protectors of Altomare and the Soul Dew. As a tale of ancient legend unfolds, involving Latias, Latios, and a duo of thieving sisters, Satoshi must thwart the villains' sinister plot to safeguard the city from impending catastrophe.