Somewhere in the world, or at least in Kommo-o's heart, exists a dark rival it is fated to confront; a rival it must defeat, for the fate of the world depends on it. Some have equated their rival with Hydreigon, noting the symmetry in their typing; others have seen it as Giratina, Yveltal, or another pokemon god that haunts human dreams. And this rivalry is not simply a matter for human speculation, some anthropomorphization projected upon this species out of Alolan legends, arising from the hopes and fears of Alolans.

Kommo-o believe their loud, six-scaled tail can not only identify their destined foe, but read the hearts of pokemon and men. Every time a Kommo-o battles, it seizes its first opportunity to strike its current opponent with its tail – and once it does, its demeanor notably changes. Kommo-o are proud pokemon, and they will still try to win, but they will typically no longer battle with the same kind of righteous, heroic passion; typically, because there are only a few living things with hearts so dark that a Kommo-o feels any need to confront them.

No Kommo-o has yet discovered its rival, and few have ever had the occasion to put their combat prowess to use in driving the darkness away. And yet, for some reason, the lands the Kommo-o call home always seem more peaceful and carefree than the rest of Alola, with any would-be "great darknesses" easily defeated. Perhaps Kommo-o has not met its rival because it does not and will never exist, for it has trained so hard and grown so strong that no villain could ever hope to confront it; after all, the nightmares of imagination, in their own way, are even greater than the horrors of history.