Control over the evil in an entire galaxy? That certainly sounds impressive, but the giant whale Kyogre hardly has anything to do with that. Its power may be less vast, but it's certainly more than enough to fell the Profound Darkness, who once was slain by beings with far less of a blessing than the ruler of all waters. Kyogre's strategy will be very simple: outspeed the vile being, open with Calm Mind to render Shadowbreaths ineffective, and then begin stalling. Once he has fully buffed his defenses and offenses, stopping to rest here and there, his Waterspouts will be so potent even Profound Darkness's multitude of forms will fall in a single torrent. Unintuitive, sure, but true, and Kyogre certainly will enjoy getting a victory against a former Godlike champion.