Kyogre helps summon lasting rain in Pokémon Pokopia.
Early in the story, Ditto needs rain to soften rock and free an Onix trapped in a cave. Tangrowth explains that Slowpoke’s yawns can bring a brief rainfall, but that first shower is not enough to solve the larger problem.
The rainfall awakens Kyogre, a Legendary Pokémon resting at the bottom of the sea. With Kyogre’s help, a proper rain is summoned, allowing Ditto to rescue Onix and continue restoring the region.
Kyogre is a Water-type Legendary Pokémon traditionally associated with the sea and rain. Groudon is its famous counterpart and is linked with land and drought, which makes it an especially plausible but incorrect answer to this question.