Kyogre summons the longer rain needed to free Onix in Pokémon Pokopia.
The story begins with an Onix trapped in a cave that is too tough for Ditto to break through. Tangrowth suggests finding Slowpoke because its yawns can summon rain. Slowpoke does produce a brief rainfall, but it is not enough to solve the problem.
That short rainfall awakens Kyogre, a Legendary Pokémon resting at the bottom of the sea. After Ditto befriends Kyogre, Kyogre helps summon a proper, sustained rain that softens the rock and allows Onix to be freed.
The distinction between Slowpoke and Kyogre matters. Slowpoke starts the chain of events by causing a brief shower, while Kyogre provides the substantial rain required for the rescue.