Kyogre awakens after Slowpoke summons rain in Pokémon Pokopia.
During the story, Ditto encounters an Onix trapped in a cave that is too difficult to break through. Tangrowth suggests that rain could soften the rock, but the region has not experienced rainfall for years. The solution is to find a Slowpoke, whose yawns can summon rain.
The initial rainfall is brief, but it is enough to awaken Kyogre from its resting place at the bottom of the sea. After Ditto befriends Kyogre, the Legendary Pokémon helps summon a more substantial rainstorm, allowing Onix to be freed.
This sequence draws on Kyogre’s established association with the sea and rainfall. It is not Groudon, whose Pokémon lore is linked to land and drought; that contrast is one reason the scene fits Kyogre particularly well.