Kyogre awakens after Slowpoke helps bring rain in Pokémon Pokopia.
During the Withered Wasteland storyline, Ditto encounters an Onix trapped inside a cave that cannot easily be opened. Professor Tangrowth explains that rain might soften the surrounding rock, but the area has not received rain for years. The solution involves finding Slowpoke, whose yawns are said to summon rain.
Slowpoke produces a brief rainfall, and that event awakens Kyogre from its resting place beneath the sea. Kyogre then helps summon a much more useful rain, allowing Ditto to free Onix and continue restoring the world.
Kyogre is particularly fitting for this sequence because it is the Legendary Pokémon traditionally associated with oceans and rain. Groudon is linked with land and drought, while Rayquaza is associated with the sky, so neither is the Legendary Pokémon awakened in this Pokopia event. Befriending Kyogre also raises Ditto’s Trainer rank enough to open Bleak Beach and Rocky Ridges.